单选题 We are disappointed to know that by the time the delegate arrived, the meeting had ______ started.
A. still
B. already
C. once
D. yet

【正确答案】 B

【答案解析】高级问题西所有选项都是副词。still主要用于现在时；once用于过去时；yet主要用在否定句中。知道这些的话就能把错误答案一个个排除了。正确答案是用于完成时的already。
[高频词语] by the time (when) S+V…，S+V… 当……的时候，……