⑴How are you? ____                                          A. I'm going by plane.

⑵Which season do you like best?____              B. I often go hiking.

⑶How are you going to Kunming?____            C. You're welcome.

⑷What do you do on the weekend?____          D. I like winter best.

⑸Whose skirt is this?____                                  E. Fine.

⑹Did you watch TV last night?____                   F. Twenty yuan.

⑺Thank you!____                                               G. Yes, I did.

⑻How much are the shorts?____                      H. It's Sarah's.

⑼What is he like?____                                       I. Sixteen.

⑽How many erasers do you have?____            J. He is old and fat.

四面体的顶点和各棱中点共有10个点，取其中不共面的4点，不同的取法共有____ 种．

辨别下面所叙述的几种事实

①一个乳酸菌　

②培养皿中的乳酸菌菌落　

③培养基被污染后，除乳酸菌外，又滋生了真菌以及大肠杆菌等其他细菌．

回答下列问题：它们各属于生命系统的哪项结构层次？

①____ ；②____；③____．