_________  __________(聚精会神) writing an essay, he couldn’t go with us.
It ________  _______(有道理) to work on the problem before it get out of control.
This club ________  ________ (由…组成) more than 200 members.
The elevators in the building are always _________  _______(出故障).
When I returned to my office, I found my desk _________(remove).
The teachers request the students remain _________(seat) when they are in class.