Both are grammatically correct. Concerning 'b', you can also use 'were'. Michael Swan 3rd edition indicates such a point and explains it in detail page 522. He says, "In English a verb normally agrees with the subject of a sentence, not with a following complement."
- The biggest time-wasteris meetings.
He goes on saying, "However, if the subject is a long way from the verb,people sometimes makethe verb agree with a complement." and then he comes to the answer to your question saying, "This often happens, too, when the subject is a relative what-clause, especially when the complement is long."
- What I am most interested in is/are your immediate personal reactions. - What we need is/are a few bright young engineers.
Thanks a lot for your cooperation .What about this sentence
1-Wheat varieties are what we are interested in.
I ask if I can say .......................................................
2-What we are interested in is wheat varieties .
Notice you have just said ........
if the subject is a long way from the verb,people sometimes makethe verb agree with a complement."
Thanks a lot .
Of course you can. What you need to focus on is "This often happens when the subject is a relative what-clause, especially when the complement is long." Can't you see that your question is very close to Swan's example above? I mean this example:
- What I am most interested in is/are your immediate personal reactions.
BTW, if you want to know about what Fowler says about 'singular what' and 'plural what', you can read this:
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