QUESTION: Animals come in all types, some fly thanks to their lightweight hollow what?
Options:
- tails
- bones
- eyes
- heads
- bodies
ANSWER: Let me think step-by-step: Birds are warm blooded vertebrates with lightweight hollow skeleton. Skeleton means bones. So the answer must be bones.

QUESTION: Where would an apple tree be near the grave site of Nelson Mandella?
Options:
- sunshine
- closer
- south africa
- bloom
- fields
ANSWER: Let me think step-by-step: Nelson Mandela was the former President of South Africa. So the answer must be south africa.

QUESTION: It was a ridiculous answer to a simple question.  The professor expected something loss convoluted and more what?
Options:
- solemn
- straightforward
- pensive
- somber
- serious
ANSWER: Let me think step-by-step: Straightforward answers should be given for a simple question. The answer was ridiculous means it was not a straightforward answer. Professors generally prefer simple answers for simple questions. So the answer must be straightforward.

QUESTION: People often describe what as a giant wall of water?
Options:
- backpack
- allen key
- snowball
- ocean
- tsunami
ANSWER:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Let me think step-by-step: Tsunami is a giant wall of water. People often describe tsunami as a giant wall of water. So the answer must be tsunami.