副词在句中起状语作用，故如果起状语作用的部分为一个句子，那么该句便是副词性从句，也称状语从句。状语从句可细分为：时间、地点、条件、原因、让步、目的、结果、比较、方式等。

　　状语从句的测试重点为：考查考生对主从句之间逻辑意义关系的把握，看其是否能选择正确的从属连词。

　　1.条件状语从句的常考知识点

　　(1)if与unless的用法。 if和unless都是引导条件状语从句的连词，考生应尤其注意unless的用法，因为它表示反面条件，相当于if not“如果不”、“除非”。如：In debating, one must correct the opponent’s facts, deny the relevance of his proof, or deny that what he presents as proof, if relevant, is sufficient.

　　(2)复合连词as long as，so long as，as far as，on condition that，in the event that;动词及分词provided(that)，providing(that)，given that, suppose/supposing(that)，assuming，say等引导条件状语从句。如：

　　You can arrive in Beijing earlier for the meeting provided you don’t mind taking the night train.

　　Assuming he is diligent in his studies at ordinary times, he is sure to pass the test.

　　In the event that she has not been informed, I will tell her. (如果……)

　　You can go swimming on condition that you don’t go too far from the river bank. (如果……)

　　Suppose it rained, we would still go. (假如……) Say it were true, what would you do about it? (假如……)

　　(3)祈使句表示条件。如：Dress warmly, or else you’ll catch cold.

　　Talk to anyone in the drug industry, and you’ll soon discover that the science of genetics is the biggest thing to hit drug research since penicillin was discovered.