circle n．圆周，圆形物，派系，循环 v. 围，环绕，盘旋
例句：I need experience to get a job, but without a job I can't get experience—it' s a vicious circle．
我得有经验才能找到工作，可是没有工作我就无法获得经验一这真是个恶性循环。

circular adj. 圆形的，循环的 n．函件通知
例句：Jim can compute the circular area with radius.
吉姆能用半径计算出圆的面积。

circuit n. 电路，一圈，周游，巡回
例句：The rocket did one circuit of the earth and returned to the earth.
火箭绕地球运行一周后返回地球。

circulate v. （使）流通，（使）运行，（使）循环，（使）传播
例句：Please open a window to allow the air to circulate.
打开窗子让空气流通。

circulation n．循环，流通，发行量
例句：The newspaper' S circulation has trebled since last year.
去年以来该报的发行量已增加到原来的三倍。

circumference n. 圆周，周围
例句：An arc isa part of the circumference of a circle or other curved lines.
弧是圆周或曲线的一部分。

circumstance n. 环境，详情，情况
例句：Due to circumstances beyond our control the lecture was cancelled.
由于无法控制的情况，讲座取消了。

diameter n. 直径
例句：The diameter of Mars is slightly over half that of the earth.
火星的直径比地球的半径稍大些。