"Everything happens for the best." my mother said whenever things weren't going my way. "Don't worry. One day your luck will change."

    I found mom was right after I finished my college education. I had decided to try for a job in a radio station. I wanted to host a sports program one day. I went to Chicago and knocked at the door of every station. But I got turned down every time.

    In one station, a kind lady said my problem was that I hadn't got enough experience." Get some work in a small station and work your way up," she said.

    I went back home. I couldn't get a job there, either. I felt really down. "Your luck will change," Mom said to me. I tried another radio station in Iowa. But the owner told me he had already had someone. As I left his office, I asked, "How can someone be a sports announcer (播音员) if he can't get a job in a radio station?"

    I was waiting for the lift when I heard the man call. "What did you mean? Do you know anything about football?" He put me in front of a microphone and asked me to try to imagine that I was giving my opinion on a football game, I succeeded.

    On my way home, Mom's words came back to me," One day your luck will change, Son. And when it happens, you'll feel doubly good because of all the hard work you've had." At that moment I knew just what she meant.

如图所示，是绿叶在光下制造有机物的实验，请回答下列问题：

（1）把盆栽的天竺葵黑暗处理一昼夜，其目的是____ 。
（2）用黑纸遮光，目的是使遮光部分不进行____ ，起到____ 作用。
（3）将叶片隔水加热，叶片逐渐由____ 色变成____ 　色。
（4）滴加碘液染色后，叶片见光的部分变成____ 色，原因它是进行了____ ，产生了____ ；遮光部分呈____ 色，原因是没有进行____ ，没有产生____ 。
（5）这个实验所要探究的变量是____ 。

古代教育家孔子说：“学而不思则罔；思而不学则殆”。这句话告诉我们（    ）

A、B两球沿一直线运动并发生正碰，如图所示为两球碰撞前后的位移时间图象．a、b分别为A、B两球碰前的位移图象，C为碰撞后两球共同运动的位移图象，若A球质量是m=2kg，则由图象判断下列结论正确的是（   ）