单选题 Various machine parts can be washed very clean and will be as clean as new ones when they are treated by ultra-sonics (超声波).
【正确答案】 B
【答案解析】[解析] 本句首先是由when引导的状语从句，其次是主句有两个并列的谓语部分：can be washed very clean及will be as clean as new ones。