下列有关血管的叙述中，正确的是（    ）

某同学利用托盘天平、玻璃杯、水、细棉线、记号笔，测出一块小石块的密度，他主要实验步骤如下：

（1）用调好的天平测出石块的质量m₁，并记录在表格内；

（2）在玻璃杯中倒入适量水，用细棉线系住石块缓慢地 ____在水中，标记此时水面的位置，用天平测出玻璃杯、水和石块的总质量为m₂，并记录在表格内；

（3）取出石块，再向玻璃杯中加水，使水面回到标记的位置，然后再用天平测出玻璃杯和水的质量m₃，并记录在表格内；

（4）石块的密度的表达式为ρ_石= ____

阅读下面短文，从短文后所给的A、B、C、D四个选项中选出能填入相应空白处的最佳选项。

Dear Sally,

    How are you? I'm happy that you can do the things you 1 at home. I never have fun, because there are too many 2 in my family. My parents are strict. I have to 3 at six o'clock every morning. And I have to make my bed 4 before breakfast and then go to school. I can't play with my friends after school. I have to do 5homework. After dinner I have to take the dog for 6 walk in the park. I can't watch TV on school nights. I have to 7 the violin for an hour. I can't go to bed late. I have to be in bed 8 nine o'clock. On weekends I have to clean my room and 9the dishes. I also have to go to learn the violin on Sundays. I'm 10 tired. Can you help me?

Yours,

Lisa