We'd better grow the plant in a ________ plastic box so that the children can see the roots growing.

(2013·福建毕业班质量检查)—What does PM 2.5 mean?—It's a professional ________ indicating the condition of air pollution.

It is very important for us to employ a word or a phrase according to the ______ in language studies.

If the time is    ________    exactly, the paper can be finished on time.

 I threatened to report the taxi driver for illegally ______ a passenger, but he pointed at his “Not for Hire” sign and drove away.