Hi Hanuman. I would say in the first one, the a) and in the second one, it depends: who's saying "He gave me a book"?, if you're saying it is b). If is not you, is a)
Both a and b are correct for the first sentence. "Did Seelu catch a cold ?" is interrogative and "Did Seelu not catch a cold?" (or Didn't Seelu catch a cold?) is negative interrogative.