阅读下面材料，在空白处填上适当的内容（1个单词）或括号内单词的正确形式。将答案填写在答题纸的相应位置。
Long long ago, there was a small village in the Middle East. In the village there was an old man called Sthira. He lived by ____(he). His only son had ____(go) far away to study. Sthira's friends wondered whether his son would return, But Sthira always said, "Whatever happens, happens for good.”
One day ____ old man's son returned and the villagers were very happy for Sthira. He thanked them and said ____(polite), "Whatever happens, happens for good.” ____, later, Sthira's son broke his leg. Once again the villagers came to visit him and once again the old man thanked them and said, "Whatever happens, happens for good."Some of the villagers were surprised ____ (hear) this. Why? What was good? His ____(son) leg got badly hurt!
After a few days, the army came to the village and forced all the young ____(man) to join the army. When they found his son had a broken leg, they left him ____. Once again, all the villagers came to congratulate him on his good luck. Like always, the old man was still ____(thank) to them and said. “Whatever happens, happens for good.”
匀速转动，下列关于小球受力的说法中正确的是： 