根据句意及首字母提示补全单词.

1. There is n_______ on the desk, but I saw  my pen just now.

2. Would you m_______ helping me with my maths ?

3. He a_______ to join us next week.

4. I'd like some w_______ to drink.

5. He g_______ me some cakes yesterday.

生物体的下列结构需要利用光学显微镜才能观察到的是（　　）

A．病毒

B．消化系统

C．叶片上的气孔

D．运动系统