④ Point out the type of adverbial clause in each of the following complex sentences.1) If you take the subway, you'll save money and time.2) The project was completed earlier than we had expected.3) She came into the room when the meeting was going on.4) We sent the letter by airmail in order that it might reach them in good time.

本题考查对不同类型状语从句的识别和判断。解题思路是根据从句在句子中所起的作用以及引导词的特点来确定状语从句的类型。

1. 对于句子 “If you take the subway, you'll save money and time”：
   • 从句 “If you take the subway” 中，“if” 是引导条件状语从句的常用连词，它表达了一种假设的条件，即“如果你乘坐地铁”，在这个条件满足的情况下，主句“you'll save money and time”（你将节省金钱和时间）的情况才会发生。所以 “If you take the subway” 是条件状语从句。
2. 对于句子 “The project was completed earlier than we had expected”：
   • 从句 “earlier than we had expected” 中，“than” 是比较状语从句的典型引导词，它用于将“项目实际完成的时间”和“我们预期的时间”进行比较，说明项目完成得比预期更早。所以 “earlier than we had expected” 是比较状语从句。
3. 对于句子 “She came into the room when the meeting was going on”：
   • 从句 “when the meeting was going on” 中，“when” 是引导时间状语从句的常用连词，它表明了主句“她走进房间”这个动作发生的时间，即“当会议正在进行的时候”。所以 “when the meeting was going on” 是时间状语从句。
4. 对于句子 “We sent the letter by airmail in order that it might reach them in good time”：
   • 从句 “in order that it might reach them in good time” 中，“in order that” 是引导目的状语从句的常用短语，它表达了主句“我们通过航空邮件寄信”的目的，即“为了信能及时到达他们手中”。所以 “in order that it might reach them in good time” 是目的状语从句。