Please answer the given financial question based on the context.
Context: |(In millions, except percentages and per share amounts)|2019|2018|2017|Percentage Change 2019 Versus 2018|Percentage Change 2018 Versus 2017|
|Revenue|$   125,843|$  110,360|$  96,571|14%|14%|
|Gross margin|82,933|72,007|62,310|15%|16%|
|Operating income|42,959|35,058|29,025|23%|21%|
|Net income|39,240|16,571|25,489|137%|(35)%|
|Diluted earnings per share|5.06|2.13|3.25|138%|(34)%|
|Non-GAAP operating income|42,959|35,058|29,331|23%|20%|
|Non-GAAP net income|36,830|30,267|25,732|22%|18%|
|Non-GAAP diluted earnings per share|4.75|3.88|3.29|22%|18%|
Non-GAAP operating income, net income, and diluted earnings per share (“EPS”) exclude the net tax impact of transfer of intangible properties, the net tax impact of the TCJA, and restructuring expenses. Refer to the Non-GAAP Financial Measures section below for a reconciliation of our financial results reported in accordance with GAAP to non-GAAP financial results.
Fiscal Year 2019 Compared with Fiscal Year 2018
Revenue increased $15.5 billion or 14%, driven by growth across each of our segments. Intelligent Cloud revenue increased, driven by server products and cloud services. Productivity and Business Processes revenue increased, driven by Office and LinkedIn. More Personal Computing revenue increased, driven by Surface, Gaming, and Windows.
Gross margin increased $10.9 billion or 15%, driven by growth across each of our segments. Gross margin percentage increased slightly, due to gross margin percentage improvement across each of our segments and favorable segment sales mix. Gross margin included a 5 percentage point improvement in commercial cloud, primarily from Azure.
Operating income increased $7.9 billion or 23%, driven by growth across each of our segments.
Key changes in expenses were:

• Cost of revenue increased $4.6 billion or 12%, driven by growth in commercial cloud, Surface, and Gaming.

• Research and development expenses increased $2.2 billion or 15%, driven by investments in cloud and artificial intelligence (“AI”) engineering, Gaming, LinkedIn, and GitHub.

• Sales and marketing expenses increased $744 million or 4%, driven by investments in commercial sales capacity, LinkedIn, and GitHub, offset in part by a decrease in marketing. Sales and marketing expenses included a favorable foreign currency impact of 2%.
Current year net income included a $2.6 billion net income tax benefit related to intangible property transfers and a $157 million net charge related to the enactment of the TCJA, which together resulted in an increase to net income and diluted EPS of $2.4 billion and $0.31, respectively. Prior year net income and diluted EPS were negatively impacted by the net charge related to the enactment of the TCJA, which resulted in a decrease to net income and diluted EPS of $13.7 billion and $1.75, respectively.
Fiscal Year 2018 Compared with Fiscal Year 2017
Revenue increased $13.8 billion or 14%, driven by growth across each of our segments. Productivity and Business Processes revenue increased, driven by LinkedIn and higher revenue from Office. Intelligent Cloud revenue increased, primarily due to higher revenue from server products and cloud services. More Personal Computing revenue increased, driven by higher revenue from Gaming, Windows, Search advertising, and Surface, offset in part by lower revenue from Phone.
Gross margin increased $9.7 billion or 16%, due to growth across each of our segments. Gross margin percentage increased slightly, driven by favorable segment sales mix and gross margin percentage improvement in More Personal Computing. Gross margin included a 7 percentage point improvement in commercial cloud, primarily from Azure.
Operating income increased $6.0 billion or 21%, driven by growth across each of our segments. LinkedIn operating loss increased $63 million to $987 million, including $1.5 billion of amortization of intangible assets. Operating income included a favorable foreign currency impact of 2%.
Key changes in expenses were: • Cost of revenue increased $4.1 billion or 12%, mainly due to growth in our commercial cloud, Gaming, LinkedIn, and Search advertising, offset in part by a reduction in Phone cost of revenue. • Sales and marketing expenses increased $2.0 billion or 13%, primarily due to LinkedIn expenses and investments in commercial sales capacity, offset in part by a decrease in Windows marketing expenses. • Research and development expenses increased $1.7 billion or 13%, primarily due to investments in cloud engineering and LinkedIn expenses. • General and administrative expenses increased $273 million or 6%, primarily due to LinkedIn expenses.
Fiscal year 2018 net income and diluted EPS were negatively impacted by the net charge related to the enactment of the TCJA, which resulted in a decrease to net income and diluted earnings per share of $13.7 billion and $1.75, respectively. Fiscal year 2017 operating income, net income, and diluted EPS were negatively impacted by restructuring expenses, which resulted in a decrease to operating income, net income, and diluted EPS of $306 million, $243 million, and $0.04, respectively.
Question: Why did research and development expenses increase in 2018?
Answer:
Research and development expenses increased $1.7 billion or 13%, primarily due to investments in cloud engineering and LinkedIn expenses.