article: There are twelve months in a year. My favorite month is October.
  October 1st is National Day . We have a seven-day holiday. During the holidays, my parents often take me to see my grandparents.
  There are also some interesting school activities in October. On October 12th, we have a soccer game. I don't love basketball because it's difficult for me. But I love soccer. I love playing soccer and watching soccer games. We have a book sale on October 20th. I have three old books and I want to sell them. The art festival is fun. We have it on October 29th. My birthday is also on this day. October is a really great month for me.
question: The writer wants to sell his three old books on   _  .
options: October 1st October 12th October 20th October 29th