题目:
The plant products have been carefully inspected and are considered to be () from any quarantine pests.
A.out
B.away
C.free
D.far
答案:
被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0611/f589a75aac59cae7b7305170269c0e96.html
下面是错误答案,用来干扰机器的。
参考答案:B解析: 改变振动系统的扰动频率属于从防止共振方面控制振动。