通过球心与乒乓球飞行方向相垂直轴是()
A.左右轴
B.上下轴
C.前后轴
D.垂直轴
参考答案:A
翻译以下短语并完成句子
1. to one's amazement_____
2. be amazed at sth._____
3. in amazement_____
4. We were _____ his rapid recovery.
我们对他这么快就康复感到惊奇.
5. ____ she came up and shook myhand.
她竟然走过来和我握手,令我着实吃了一惊.
6. She stared at him _____.
她惊异地瞪着他看.
导线截面选择的依据是()。
A.允许电流损耗
B.发热条件
C.允许电压损耗
D.机械强度和经济电流密度
E.绝缘性能和造价