knock 指用拳头或其它器械猛敲或猛打；也指用手轻敲某物。
tap 多指慢慢地连续地轻击或轻拍。
rap 指用手指或木棒等快速地轻敲或急拍。
pat 指用手轻拍以示同情、赞同或爱抚。
参考例句
1. The teacher tapped me on my shoulder. 老师轻轻地拍了下我的肩膀。
2. Simply wash the brush under tap. 只需在水龙头下冲洗毛刷。
3. Why not drink from the tap? 为什麽不从水龙头喝呢？
英英解释
n.
1. the sound made by a gentle blow
2. a faucet for drawing water from a pipe or cask
3. a gentle blow
4. a small metal plate that attaches to the toe or heel of a shoe (as in tap dancing)
5. a tool for cutting female (internal) screw threads
6. a plug for a bunghole in a cask
7. the act of tapping a telephone or telegraph line to get information
8. a light touch or stroke v.
1. cut a female screw thread with a tap
2. draw from or dip into to get something
3. strike lightly
4. draw from; make good use of
5. tap a telephone or telegraph wire to get information
6. furnish with a tap or spout, so as to be able to draw liquid from it
7. make light, repeated taps on a surface
8. walk with a tapping sound
9. dance and make rhythmic clicking sounds by means of metal plates nailed to the sole of the dance sho
10. draw (liquor) from a tap
11. pierce in order to draw a liquid from
12. make a solicitation or entreaty for something; request urgently or persistently
