The boy found _____ easy to fly kites. [ ]
A. that
B. it
C. this
答案：B
We can't late for class.[ ]
A. get to
B. arrive at
C. arrive in
D. arrive
机械密封发生周期性或阵发性泄漏原因之一是（）。
A.弹簧压缩量太小
B.密封端面宽度太小
C.转子组件轴向窜量太大
D.不以上均不正确
