1)False, because NP-complete problems are those for which we don't have efficient(polynomial time) algorithm but still, it has not yet mathematically proven that we can never solve efficiently. i.e. we may solve it efficiently in that case P=NP
2) True because from the definition of NP-Complete problem it follows "NPC problems are set of problems in NP that are as hard as any problem in NP"
3)False, Checking whether a number is a prime is in P. This a famous groundbreaking work by prof Manindra Agrawal of IIT-K and his two undergraduate students namely AKS primality testing algorithm which shows that testing whether a number is a prime is in P
For more details about AKS algorithm, you may refer this: https://en.wikipedia.org/wiki/AKS_primality_test
Hence, Option B is the correct answer