2) 条件状语从句
　　条件状语从句主要由以下连词引导：if, unless, providing/provided (that), suppose/supposing (that), on condition (that), as/so long as, in case等。
　　So long as you work hard, you will surely achieve good results in examinations.
　　I shall return next Thursday unless something unexpected happens.
　　I will go provided that you go with me.
　　Please give this letter to John in case he comes.