根据短文内容判断下列句子正误。
    My name is Amy. Tomorrow is Saturday. My parents aren't going to work, but we are going to be very busy tomorrow. My mother is going to buy something. I'm going to the bookstore in the morning. Then I'm going to buy a dictionary.
    Tomorrow evening we are going to visit my grandparents and have a big dinner. After that we are going to the cinema. I think we are going to have a nice weekend.

如图所示的机械中，不计摩擦和绳重，属于同一类杠杆的是（   ）

①镊子               ②天平             ③定滑轮      ④开瓶器

计算．

$48\times \frac{3}{16}$ =____      $\frac{5}{21}\times \frac{3}{10}$ =____

下列物质中，不属于空气成分的是（   ）

下图显示制作洋葱鳞片叶内表皮细胞临时装片的几个步骤。请根据制作临时装片的知识回答问题