"Set of techniques"; singular or plural? [duplicate]

I have an English course book that contains this question:

Fill in the blank "The book is a set of techniques that systematically __ the learner for interaction with target language speakers".
(A) prepare (B) preparing (C) prepares (D) prepared."

The answer given in the book is A, but isn't C correct? I used Google and found this example "DNA technology is a powerful set of techniques that ALLOWS scientists to examine, change, and create new genetic material"


Solution 1:

The question comes down to who is doing the preparing:

  1. The book prepares
  2. The set prepares
  3. The techniques prepare

I’m pretty certain that the intended meaning here is one where only option 3 makes sense. Therefore, the correct verb is prepare.