Correct option is (a) Covalent catalysis
To explain I would say: Catalysis which involves substrates forming transient covalent bond with the residues present in the active site is referred to as covalent catalysis. If the catalysis involves participation of small organic molecules, co-factors and amino-acids side chains from the enzyme is referred to as general acid-base catalysis. If the catalysis involves water molecules for proton donation or acceptance, the catalysis is referred to as general acid-base catalysis. Lock and key model proposes that as a key fits into a lock same way, substrate fits into the enzyme.