Your doubt are well founded. None of the answers are correct.
I suspect answer 'a)' is supposed to say "reduce the impedance at the input" or similar which would make it the correct selection but 'ressonance' has nothing to do with it.
it is possible question 1 intends to say D1. Two of the answers sound like they are more applicable to the application of diodes than to capacitors. One of these statements would be correct if C1 is replaced with D1.
For question 2, a/b are technically true statements. However not normally for components used in this circuit and at these frequencies.