Question

True or false according to the principle of base pairing hydrogen bonds could form only between adenine and cytosine

Answer 1

Answer is: false.
According to the principle of base pairing hydrogen bonds could form between adenine and thymine (two hydrogen bonds between this nucleobases) and guanine and cytosine (three hydrogen bonds between this nucleobases).
Adenine and guanine are purine derivatives and thymine and cytosine are pyrimidine derivates.