问题补充：
All the students at school are required to lectures by the experts on howto save themselves when accidents occur, such as fires, a gas leak and so on.
A. join in
B. take part in
C. attend
D. participate in
答案：
A. join in
B. take part in
(答案→)C. attend
D. participate in
解析：当作参加讲时join和 take part in是相同的，都表示加入某种组织、政党、俱乐部等团体（join a club.成为俱乐部的会员） 但是用法上，take part in 不可以用被动语态。attend 是出席的意思，表示在某种比较正式的场合出现。例如，上课，会议等。
join in +(加入一个组织)join in the organization
join （join us/参与*一起*的活动)join us to watch TV
take part in (参加一项活动)Take part in the sports meeting.
Lecture是演讲的意思，因此选C 最合适。
