次生演替(secondary succession)

电力用煤的采制化过程中，常用工业实验筛孔径有多少种？

50年代我国提出的外交方针、原则，至今仍富有生命力并被广泛应用的是

①“求同存异”的方针 ②反对霸权主义强权政策

③和平共处五项原则 ④发展与第三世界国家的友好合作关系 [ ]

A．①②③

B．②③

C．①③

D．③④

用适当的介词填空。

1. Every sportsman is training hard ________ the Beijing Olympics.

2. There are many different theme parks ________ the world.

3. Liu Xiang is a symbol ________ China's international sporting success.

4. If you are a famous sportsman, you'll be asked to appear ________ advertisements, films and so on.

5. ________ other sports stars, Wang Hao started training when he was very young.

6. Du Li won the first gold medal ________ China at the Athens Olympics.

7. Zhang Yining doesn't want to spend too much time away ________ sport.

8. Wang Bilin noticed Zhang Yining's skill ________ playing table tennis.

关于卵巢Krukenberg瘤的描述，正确的有哪些（）.

A.影像学多为单侧卵巢实性肿块

B.易发生于40～50岁，转移瘤症状较原发瘤更明显

C.生长迅速，预后极差

D.原发瘤多为胃肠道肿瘤，也可见于乳腺肿瘤

E.是含大量印戒细胞的转移瘤

已知某工程网络计划的计算工期等于计划工期，且工作N的紧后工作均为关键工作，则N( )。

A．总时差为零

B．自由时差等于总时差

C．自由时差为零

D．自由时差小于总时差