All are unacceptable structures. These are better but still awkward. Cleft sentences are studied much more often than they are used. I don't know why they are so popular with learners.
a. It was to him that she gave the book b. It was when he did it that she didn't know. c. It was to our room that the boy took us
Thank you for the answer. And it seems that the native speakers usually don't use this kind of structure in both real situations and the formal writing. That is what you mean by the expression 'awkward', I think. Is it right? Or else the grammaticality iteslf of these three sentences is somewhat wrong. Is it so?