Option A is correct.here public key(e =5,n=35) so we first choose two distinct prime number p and q such that n = p *q. So we find p=7 and q=5, now we will have to find phi(n)=p-1 * q-1 = 6*4=24.
So public key is given (e=5,n=35),now we will find 5*d mod 24 =1.on checking options d=5 satisfy the remainder 1....
So (5,35) is the answer.