当细胞进入M期后下列哪些现象不发生（）。 A.染色质浓缩 B.组蛋白和H1脱磷酸化

已知数列{a_n}满足a₁=33，a_n+1-a_n=2n，则a_n=______．

Dear Mr White,

I am writing tell you a piece of good news. Last week our school hold a Spoken English Competition. I stood out in the competition and won a first place. In my view, it is your kind help which has helped me gain the achievement. During your spare time, you often spent such much time helping me with your spoken English that I made rapid progress. In the competition, I followed your advices on how to behave, which led to my success. I’m grateful to you for your help and decide that I will make up more efforts and try to make great progress in the future.

I’m looking forward to hear from you soon.

Yours sincerely,

Li Hua

A、B、C、D四种元素在周期表中分别处于元素X的四周（如下右图），已知X元素最高价氧化物的化学式为X₂O₅，且五种元素中有一种元素的原子半径是它所处族中最小的．请回答下列问题：

（1）写出各元素的符号：A______，B______，C______．

	B
A	X	C
	D

（2）写出A、X、C最高价氧化物对应水化物的酸性由强到弱的顺序（最高价氧化物对应水化物用化学式表示）：______．

（3）写出A、B、X气态氢化物稳定性由强到弱的顺序（气态氢化物用化学式表示）：______．

一般来说，经过对广告代理商的资质考察，出现在初选名单上的代理商应该是（）个，每一家广告代理商都应该符合企业所设立的标准。

A.2~3

B.4~6

C.8~10

D.10~15

有关骨盆底，正确的是（）

A.骨盆底的前方为耻骨联合上缘，后方为尾骨尖

B.骨盆底分前后两部，前部为尿生殖膈三角，后部为肛门三角

C.骨盆底浅层中只有3对肌肉

D.骨盆底结构和功能发生异常可影响盆腔器官但不会影响分娩

E.骨盆底最内层的坚韧层称为泌尿生殖膈