1. Write down your activities. Which are more important? Do them.

Question

2. Write down your activities. Which is more important? Do them.

(Which one is right? Do we have to use 'Which are' or 'Which is'?)

3. Summer break is over.
4. Summer vacation is over.
5. Summer holiday is over.
(If a student says the expressions above, do they have the same meaning? [from 3-5])

Answer 1

#1 is right if there are three or more activities or maybe an unknown number of activities.

#2 is right if there are only two activities (no other number!).

"Which are" is correct since you're referring to "activities" (plural).

3 - 5 are all about the same, yes.

Answer 2

You would use "Which is" if you want to choose just one.

If you may choose more than one, you would use "which are".

3-5 all mean the same thing and all are used.