若生殖细胞内染色体数目为n．从亲代到生殖细胞再到子代，细胞中染色体数目变化规律是（　　）

 在21世纪初，我国成功的承办了一次国际性的会议，请你回答这次会议的名称是什么？以及此次会议的背景、具体时间与地点、主题、参会主要领导人以及会议取得的成果。

-----What do you suppose_______her look so upset ?
----- _______by her boyfriend again.

已知函数f（x）=x³+ax²+bx（a，b∈R）的图象如图所示，它与直线y=0在原点处相切，此切线与函数图象所围区域（图中阴影部分）的面积为 $\frac{27}{4}$ ，则a的值为____．

先通读下面的短文。掌握其大意，然后从A、B、C、D四个选项中选择可以填入空白处的最佳答案。
    In order to quit smoking(戒烟)，Cheyenne Lu has been living in a glass box on a busy shopping street for three days．
    Lu has been smoking for the last 12 years,and she1 how difficult it is to quit．She tried many times before，but all failed(失败)．One main 2 was that she didn't tell her family and friends that she was trying to give up(放弃)．So this time she told them her decision．
    Lu has been eating and sleeping in a glass box3a computer and some DVDs helping her pass the time．She has been keeping all online diary(日记)to record4experiences in the glass box．
    Lu said she got a lot of encouragement from people passing by.5, some people tried to make it more difficult by stopping in front of her window and lighting a cigarette(点烟).One stranger6offered to give her$500 to smoke a cigarette with him."Surprisingly,it made me want to stop smoking even more．"said Lu.
     7Lu hasn't smoked for three days,she knows this is only the beginning of her smoke-free journey.But she has 8to look forward to.She is a 9fan,and she plans to use all the money she saves by not smoking to travel to London．She10to see her favourite football player Cesc Fabregas in real life.