Before you decide to drop out,（）the effect it will have on y

选B,首先从语意上讲,这句话的意思是,在你决定退学之前,请考虑它对你未来的影响.从语序上讲,这句话可以调整为consider the effect it will have on your future before you decide to drop out.这样你就很容易看出这是一个简单的祈使句,祈使中动词用原形.