处于生长发育阶段的青少年适当多吃点富含蛋白质的食物，这是因为蛋白质（　　）

计算题．

① $\frac{2}{5}\times \frac{1}{2}÷\frac{2}{5}\times \frac{1}{2}$

② $\frac{1}{12}$ +（4 $\frac{5}{12}-3\frac{1}{2}$ ） $÷\frac{11}{24}$

③3.14×43+7.2×31.4﹣150×0.314

④1+3 $\frac{1}{6}$ +5 $\frac{1}{12}+9\frac{1}{30}+11\frac{1}{42}+13\frac{1}{56}\text{+}15\frac{1}{72}+17\frac{1}{90}\text{+}19\frac{1}{110}$ ．

    Last fall, before Thanksgiving, I was making my way in my car out of the shopping center parking lot. I was bored in the car. I 1 a woman heavily loaded with 2 and her two boys, one carrying a pumpkin and the other another bag.

    They were headed, I3 to the bus stop across the major road.4 it was too far to walk with all those 5 to any of the nearby bus stops, on a random impulse（冲动），I rolled down my window and asked if they were indeed headed to the6. “Yes,” the mother 7 I asked, “Would you like a 8? “Oh, yes!” was their 9reaction.

    I was also delighted，and，after driving out of the way of other10 I stopped and the boys piled into the back seat . The mother started to push 11beside them. I 12her by saying, “Oh, you come on up here 13 me. I'm not a taxi driver!” So off we went.

    Right away, I decided to take them a mile and a half to their home, since I had 14and they had bags. All the way, I had just a fine time listening and talking with all of them. It felt so good to be able to do this little 15 and showed that with such a small 16 I could make a big difference to a tired mother. I'm not sure 17got the most out of it.

    18this was special for me 19 as a disabled person, I often receive help and now I know how especially good it feels to be 20