物质的性质决定其用途。下列物质的用途中，主要利用其化学性质的是

You are____ (wave) to say goodbye.

用句子补全对话。

Black: Hi, Tom. Long time no see!

Tom:  Hi, Black. ____?

Black: Fine. Thanks for asking.

Tom:  It must be a new shirt you're wearing. ____?

Black: It's made of silk. It's very soft.

Tom:  It looks cool. ____?

Black: 100 Yuan.

Tom:  It's not very expensive. I also want to buy one. ____?

Black: I bought it at Xidan.

Tom:  OK! I like blue best.____?

Black: Yes, there is blue shirt at that store.

下列各点中，符合“西半球、北半球、低纬度”三个条件的是（    ）

对开普勒行星绕太阳运转的第三定律 $\frac{r^3}{T^2}$ =k，正确的是（   ）