854 查看正确答案
—When can I call on you, afternoon or evening? —________. I’ll be at home all the time.
446 查看正确答案
What the monitor said at the class meeting ________ quite all right．
423 查看正确答案
The room ________often cleaned by the students．
117 查看正确答案
用单色光照射金属表面，使金属释放光电子，增大单色光的频率，但同时减小它的强度，则光电子的实际动能（ ）