Correct answer is (a) Ethylmethylamine
To explain: In the common system, aliphatic amines are named by prefixing the alkyl group to amine, i.e., alkylamine. In case of two different alkyl groups, it is named by listing the alkyl groups in alphabetical order before the word amine, just like in ethylmethylamine. Aniline is a common name but is also accepted by IUPAC.