English Sentence Completion Online Test 1

Subjunctive mood is used in non-statements (wishes, demands, condition contrary to fact, suggestion and the like.) . The given sentence is a condition contrary to fact. In such case plural verb is used even if subject is singular.
He behaves as if he werea king.

Condition Contrary to fact: He is not a king, in truth, but only behaves as if he was. Other examples:
She acts as if she were his wife. (Condition Contrary to fact. She is not his wife, in truth, but only acts as if she was.)