Explanation:

Adverbs of Frequency like: always, never, often, rarely, usually, generally, and also some other adverbs like: almost, already, hardly, nearly, just, quite etc. are normally put between the subject and the verb if the verb consists of only one word; if there is more than one word in the verb, they are put after the first word. So, we need to put ‘always’ between the subject and the verb.
Also, since the subject is singular therefore the verb should also be singular. Hence, ‘sing’ should be replaced with ‘sings’.
Option (a) is the correct choice here.