分离下列各组物质，采用的方法正确的是（   ）

下列各组元素，按原子半径依次减小，元素第一电离能逐渐升高的顺序排列的是

下列各组离子在溶液中按括号内的物质的量之比混合，得到无色、碱性、澄清溶液的是

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.

如果 $\sqrt{3a+12}$是二次根式，那么a的取值范围是（　　）