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如图是HIV感染人体细胞过程的示意图。回答下列问题。

治疗艾滋病的药物AZT的分子构造与胸腺嘧啶脱氧核苷酸的结构很相似。则AZT抑制病毒繁殖的机制可能是抑制（）过程。

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单项选择题

[听力原文] 我个人认为我们中学生可以上网，因为上网不但能增长知识，还能让我们眼界宽广。最重要的是方便我们与远方的朋友交流，从而加深我们的友谊。 说话人是什么人？（）

A．老师 

B．中学生 

C．大学生 

D．小学生
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Memo
To: All the Staff
From: Mr. Mendels, the Personnel Manager
Date: Dec 15, 2008
Ref: JM/15/12/08
Subject: The granting of annual leave in the coming year
To help you plan your annual leave, I would like to clarify the company’s policies as follows :
You should apply at least two weeks in advance if you intend to take leave longer than 14 days; you should submit your proposals on how your duties can be shared by others. We expect five rush periods next year and we need to set a quota of leaves for each.
I Jan to 15 Jan-Maximum leaves, 5; 5 Feb to 20 Feb-Maximum, 4; 20 Mar to 30 Mar-Maximum,6; I May to 10 May-Maximum, 5; 15 Dec to 24 Dec-Maximum, 2.
Applications for leaves during rush periods will be granted on first-come-first-served basis until the quota is filled.
Memo
To: All the Staff
From: Mr. Mendels, the Personnel Manager
Date: Dec 15, 2008
Ref: JM/15/12/08
Subject: The (46) of annual leave in the coming year
Purpose: Help all the staff plan (47)
Company policies:
For longer than two weeks leave, apply at least (48) in advance.
Submit your (49) on how your duties can be shared with others.
Five (50) of leave for five expected rush periods.
First-come-first, go policy, until the quota is filled
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