题目

. You must have had a good time at the party last night ,didn’t you ? ______.Actually , it was a bit boring . A. Oh ,grate     B . I sppose so   C.  Not really   D. That’s Ok 答案：C7．PM2.5是指大气中直径小于或等于2.5微米的颗粒物，2.5微米等于0.000 002 5米，把数字0.000 002 5用科学记数法表示为（　　）A．2.5×106B．0.25×10-6C．25×10-6D．2.5×10-6