题目

On the first day of your Senior High you must meet many new classmates. Do you want to make friends with them? Do you know how to make friends with them? The following article will tell you how to do it. Making friends is a skill. Like most skills, it improves   21   practice. If you want to meet people and make friends you must be   22   to take action. You must first go to places where there are people. You won’t make friends   23   at home alone. Join a club or group, for talking with those who   24   the same experience as you is easier, and   25   them in s氢气的热值为1.4×108J／kg，比煤和石油要高出许多，且燃烧后的产物是水蒸气，排放到大气中不会造成污染，10kg氢气完全燃烧放出的热量是_________J；若这些热量的50％被水吸收，能使_______kg的水温度升高50℃。（已知c水=4.2×103J/（kg·℃）