a moment和the moment这两个短语的区别是：
a moment的意思是片刻，一会儿，一时，一点儿，常与延续性动词连用；the moment的意思是目前，当时。例如：
She hesitated for a moment,and then went on.她迟疑了一下，然后接着说。
There is no need to fear for him for the moment, he is going to get well.目前不必为他担忧，他很快就会好起来。
测试：
用a moment或the moment 填空：
1、The police arrived right at_____of the explosion.
2、Will you watch for the bus while I go into the shop for______?
答案：1 .the moment 2.a moment
