Nowadays, Tet (lunar New Year's festival) _________________
A. is much shorter than that in the past B. does not last longer than that in the past
The key is A, but why not B, please?
'That' doesn't belong. B could be right. It means something different, and would be an unusual thing to say. We don't go around commenting on all the things that haven't changed unless there's a reason, whereas if something has changed, that's often reason enough to comment on it.