Plenty of vegetables would be the most natural. These 'are' is the correct answer. The auxiliary verb tense goes with the subject(s), not the verb. There is a silent word in the question statement... "Playing basketball and volleyball are what he likes most." actually means Playing basketball and playing volleyball are what he likes most. Good luck - I have my fingers crossed for you

1 is easy easy as Time after Time wrote - A is. 2 C but D not wrong. Jesse misread answers.

thank you，Time After Time！:-)

plenty of vegetables... is what he likes most

I'd choose IS because it's just one action "Playing" There are two objects but just one action and the second one it's difficult haha I'll wait for someone's answer