【单选题】Don’t bother me.I am listening to the birds ______.
【单选题】在通常采用的分度头上,装夹工件的三抓卡盘是通过一定速比为1:40的涡轮,蜗杆带动的,当手柄摇过一转时,工件转过 。
【单选题】平带传动的特点有( )
D.
过载时能打滑,起安全保护作用,并能保持准确的传动比
【判断题】Aspirin的代谢主产物是水杨酰甘氨酸
【单选题】转座子引起的突变可引起类似于缺失突变的效果,导致基因功能的丧失。现有一个青霉素抗性的菌株,经过Tn5转座子的侵染后,失去了青霉素的抗性,可能的原因是( )。
【简答题】The old professor _______ something serious. Don ’t bother him now. A.seems to think of B.seems to have thought about C.seems to be thinking of D.seemed thinking about