It has become like a game of ping pong - over the years, theories have been batted back and forth as new evidence comes to light.

它变得很像一场乒乓球比赛——多年来，由于新的证据人所周知，一些理论，来来回回地讨论。

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Table tennis, also known as ping-pong, is a sport in which two or four players hit a lightweight, hollow ball back and forth using table tennis rackets.

乒乓球是一项体育运动，其中两名或四名选手用乒乓球拍来回拍击一种轻便的空心球。

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And later on if you right before or right during you give the dog some food you--you ping a bell the bell will cause the saliva to come forth.

,在喂食前或者喂食过程中,你摇铃,铃声就会加速唾液的分泌。

耶鲁公开课 - 心理学导论课程节选

Ping pong back and forth faster.

FORBES: Connect

This will result in "parliamentary ping-pong", meaning the Growth and Infrastructure Bill goes back and forth between the two Houses until a resolution is reached.

BBC: Peers reject workplace rights-for-shares scheme

Where differences of opinion between the two chambers prove difficult to reconcile, a bout of parliamentary ping-pong may ensue - so called because a bill bounces back and forth between the Commons and the Lords until both chambers approve the final wording.

BBC: Democracy Live site links