When there is an 'if' in the sentence, we may infer that the sentence is
a conditional one. When the situation is a likely/ possible one, we say
that the sentence is in the first conditional. This is the case for the
sentence given. In first conditional sentences, the 'conditional
clause/ if clause' is in the present tense, while the 'main clause' is
in the simple future tense. So, the correct answer is A) sits, will sit.