在○里填上2、4、5、6、7，使每行三个数和都为12。
实验用的托盘天平的底座做得又大又重，这是用了增加支承面和____ 的方法来使天平稳定，天平使用时要放在水平桌面上，是因为重力方向是____．
浏阳（28°N）夏至日时，为使太阳能热水器的效率最高，则太阳能热水器集热板与楼顶水平面的夹角应为（ ）
A
⑴Who are they? ____
⑵Where did you live?____
⑶Is this your grandpa?____
⑷Did he learn Chinese ?____
⑸What's he doing?____
B
A.Yes, it is.
B.They are my grandparents.
C.He's reading a book.
D.No,he didn't.
E.I lived in a small house.
