for the question 16, I don't know either using "How was your break?" or "What's going on". And Q20,"what about you?" and "what are you up to?" seem able to use? Could someone explain their usages?
1 Answer
The trick here is to look at the response to figure out what the missing preceding phrase has to be. For 16, "It was really fun" wouldn't be a response to any of the options except "How was your break?" For instance, the only proper response to "What can I do for you?" is an answer like "Nothing." or "You can give me a ride to the airport."
For 20, the response is "I went to the beach", which is in the past tense. That wouldn't be a reply to a present tense question like "What's happening?" (i.e., "What is happening?") or "How are you?"