A. go to see him         

B. have a lot of fun

C. under the tree                    

D. at Christmas

E. a Christmas tree                

F. buy presents

G. a turkey and Christmas puddings

A:What do you do ____?

B: First, we ____ for our family and friends. We need to buy____.We put our presents ____.It looks great.

A:What do you like best at Christmas?

B:I like Father Christmas. We sometimes ____.

A:What do you eat that day?

B:I eat ____ .

A:So you ____at Christmas.

阅读下面的文字，回答问题．

我们知道 $\frac{1}{1\times 2}=1-\frac{1}{2}$，$\frac{1}{2\times 3}=\frac{1}{2}-\frac{1}{3}$，$\frac{1}{3\times 4}=\frac{1}{3}-\frac{1}{4}$

如图，甲、乙分别是“探究平面镜成像的特点”和“探究凸透镜成像的规律”的实验装置。

下列变化中一定属于化学变化的是(   )