①若用氯化钠固体配制，需称取氯化钠固体7.0g

②选用200ml量筒量取所需水的体积

③实验中用到的玻璃仪器有烧杯、量筒、玻璃棒和试剂瓶

④用量筒量取水时，俯视读数，配得溶液的溶质质量分数偏小．

北风卷地白草折，____ 。（《白雪歌送武判官归京》）

如图所示，利用轻质滑轮组匀速拉动水平地面上重为300N的物体，拉力F的大小为30N，若物体和地面之间的摩擦力大小为45N，则A处的拉力大小和滑轮组的机械效率分别为（　　）

看图，读一读，将字母的序号写在横线上。

A. In winter, it is cold. The ugly duckling has no home. He is very sad.

B. Uncle Lin has a garden. There are many plants in it. He waters them every day.

C. We are three little pigs. We are clever. We are not afraid of the big bad wolf.

D. Mother Duck has some eggs. She sits on the eggs.