题干

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= ____

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    After my brother died in an accident, my mother was very sad. I was only 4 years old at the time, but I still understood the 1 in my mom's attitude toward safety.2, everything around us was potentially 3.

    I grew up with a lot of 4 and rules that were meant to 5 me. For example, I was not 6 to walk home from school by myself, even though everyone I knew already did. I couldn't 7 evening parties or go to summer camp,8 what if something happened to me?

    As I got older, the list of things to 9 got longer. I became a natural 10. I was concerned about things like getting cancer, losing my wallet, being caught in car accidents and earthquakes —11 big and small, real and 12.The funny part is that you'd never know it by looking at my life, because I'm constantly 13 myself to do the things that frighten or worry me. In fact, I've developed a 14 for myself: If it scares me, then I have to do it 15 once. I've done lots of things that would have 16 my mom: I've ridden a motorcycle, I've traveled alone, and I've performed stand-up comedy.

    Courage isn't a natural attribute (品质) of human beings. I believe that we have to practice being courageous. The more 17 I do things that scare me or that make me 18, the more I realize that I can do a lot more than I originally thought I could do.

    Even though I inherited (经遗传获得) my mother's cautious19, I've also come to believe that fear can be a good thing, if we 20 it. Believing that has made my world a less scary place.