可以由that, so that, in order that, lest, for fear that, in case等詞引導;
lest：以防;從句中的謂語動詞必須用should+動詞原形;
eg: He wrote the name down for fear that(lest) he should forget it.
He took the umbrella with him lest it should rain.
in case：以防;與lest不同，從句里的時態(tài)不做特殊變化;
eg：Take the umbrella with you in case it rains.
for feat that：和lest保持一致;
eg：A variety of activities should be organized so that participants can remain active as long as they want and then go on to something else without feeling guilty and without letting the other participants down.
let…down…：讓……感到氣餒
