bicycle/circle/semicircle/circular/circus/circuit/circulate/circumstance/cycle/cyclist/recycle/motorcycle
记忆：
1. 词根cycle表示“圆” 前缀bi-表示“二”： bicycle n. 两轮车，自行车，简写为bike. Bicycles are green to the environment. 自行车有利于环保。
2. re-表示 “又“， recycle v. 再循环，回收利用 We should recycle the used things.我们应回收利用旧东西。
3. tri-表示“三”，tricycle n. 三轮车
4. uni-表示“一”，unicycle n. 单轮脚踏车
5. motor马达；motorcycle, n. 摩托车
6. circle n. 圆，盘旋 Look! A pigeon is circling over us! 看！一只鸽子在我们上空盘旋。
7. circular adj. 圆形的 They finally completed the circular building. 他们最后完成了那座圆形大楼的建造。
8. semi -, 半 semicircle n. 半圆
9. circus n. 马戏团（外出表演时常画圈表演）Monkeys and bears are often the leading actors in a circus. 马戏团里猴子和熊常常是主角。
10. circuit n.电路, 一圈, 周游, 巡回 The circuit of the chip is very complicated. 芯片的电路非常复杂。
11. circulate To move in or flow through a circle or circuit v.(使)流通, (使)运行, (使)循环 Blood circulates through the body. 血在全身循环。
12. circumstance n. 环境, 详情, 境况 We have to suit ourselves to the new circumstances. 我们得调整自己以适应新的环境。
13. cycle n. 周期, 循环 vi.循环, 骑自行车 Have you studied your studying circle? 你研究过你的学习周期吗？
14. cyclist n. 骑脚踏车的人 The boy wants to be a professional cyclist. 这男孩想成为职业自行车手。
另类阅读：
Though the motorcycle runs faster, he prefers a bicycle to go to the circus to enjoy himself. He thinks it’s better for the environment. He also combines a bike with a bag so he can collect some wastes to recycle on his circular trip