(a) No, that's not right. This type of situation can be difficult. We have already seen that acceptance by conduct is recognised as effective. It might be argued here that doing nothing is the conduct required of B to accept A's offer. But there is another rule, which says that silence is not consent. This rule would mean that B has not accepted A's offer. Which rule applies?
The answer is that, while specific conduct can be stipulated by the offeror as the means of accepting an offer, that does not include silence or inaction. The required conduct must normally be some positive act or statement.