先看一道试题。The flowers his friend gave him will die unless____every day. A.watered B.watering C.water D.to water答案为A项,考查的是unless+过去分词作条件状语。把unless后面加上they are就是条件状语从句。 First look at a test. The flowers his friend gave him will die unless____every day. A.watered B.watering C.water D.to water The answer is item A, which examines unless + the past participle as the conditional adverbial. Adding unless after are unless is an adverbial clause.