Since the ___, the company has doubled in size.
a. 1990's
b. 1990s
c. 1990s'
d. 1990ies
After searching on Google, I think the answer is b. However, when I submit the final answer, it says that my answer is incorrect. I have been reading a lot of articles and I found that the authors are also using 1990s, 1970s, etc. Anyone can correct my understanding when mentioning the year? Thank you.