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= ____

    Hello! My name is Wendy. I live in the city. My family doesn't have a car, so I go to school on the bus. There are four people in my family. They are my parents, my brother and I. We live happily together.

    At school, I study very hard. I am very good at English. I often help my classmates with their Chinese and English. I enjoy learning.

    I am a quiet girl. I like reading and listening to light music. I have some friends. We always spend time together, they are very funny and friendly. I wish we can be friends forever.