钟式沉砂池是利用（）控制水流流态与流速，加速砂粒的沉淀并使有机物随水流带走的沉砂装置。
A．池壁阻力
B．入池水流的旋流作用
C．机械力
D．空气扩散装置
参考答案：C
解析：
污水由流入口沿切线方向流入沉砂区，利用电动机及传动装置带动转盘和斜坡式叶片，由于所受离心力的不同，把砂粒甩向池壁，掉入砂斗，有机物被送回污水中。调整转速可达到最佳沉砂效果。
综合填空：根据短文内容选择方框内的单词的正确形式填空。
Jim is a 15-year-old boy. His parents are so busy that they can’t look after him well. Last week they saw Jim 小题2: in the bedroom and found that he had a toothache. Then they took him to the 小题3:. Mr. Green looked him over carefully and was 小题4: to see that he had 16 cavities（蛀牙）. When he heard that Jim ate too much candy, he suggested that he must not eat it often, to protect（保护）his weak teeth. He also gave another common（普通的）小题5: that Jim should brush his teeth every day. At last, the dentist asked Jim’s parents to take him to see a dentist every 3 mouths. |