Answering a singular question with a plural answer

If somebody asks a question in the singular, how do we give a plural answer? Here's an example, with three different possible ways to answer. (The part of the answer that has the plural sense is marked in bold):

Q: What's the most important thing to you?

A1: The most important thing to me is my friends.

A2: The most important thing to me are my friends.

A3: The most important things to me are my friends.

I am a native speaker of British English. I prefer A1. An American told me she preferred A2. I suspect that a formal prescriptivist would recommend A3.

Is there any rhyme or reason to this? What should I recommend to a student learning English?

Solution 1:

These are cleft sentences where there is a separation the grammatical and the logical subject, and both A1 and A2 make sense.

In A1 the verb agrees with the grammatical subject: The most important thing to me (singular).

In A2 the verb agrees with the logical subject: my friends (plural).

The odd one out is A3

"The most important thing to me" as in A1 and A2 implies a single item or a single set of items.

"The most important things to me" on the other hand implies a list of (sets of) items, but "my fiends" is not a list.

Solution 2:

To a student who is learning English and is a true beginner or at elementary level, I would say that they (plural!) will hear all three forms, especially in speech. That A1 is probably what they should aim for, because the verb, be, agrees with the singular subject "the most important thing". However, they should be aware that A2:

the most important thing to me are my friends

is acceptable and many native speakers will in fact say this without blinking an eye.

Solution 3:

If you want to answer a singular question with a plural answer, most people will understand "your friends" as a set of something. But, to someone learning English, A1 might be confusing, and so they should use A3 until they become fluent. A2 is blatantly wrong.