The paper briefly introduces the history and development of the theory of activity teaching.

研究初中生物活动教学具有重要的理论与现实的意义。

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Another flaw of the tiredness theory is that yawning does not raise alertness or physiological activity, as the theory would predict.

疲劳理论的另一个缺陷是，打哈欠并不能像该理论所预测的那样，提高警觉性或生理活跃度。

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Certainly, some of the facts at hand are valid; for example, the Maya did have a Long Count calendar, pole-shift theory does exist, and solar activity does wax and wane.

当然，有些事实证据是有效的，比如玛雅人的确有一个长记历的历法，地磁反转理论也的确存在，太阳活动的确在减弱等等。

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The discovery of quantum mechanics and Einstein's theory of relativity, vital to much of modern technology and economic activity, including the transistor, the laser and the atomic bomb.

ECONOMIST: Letters

With a mobile network that offers broadband speeds and capacity, it in theory becomes possible to carry out all manner of online activity on the hoof.

CNN: 4 ways 4G will change your life

The resulting photosynthetic activity could, in theory, increase the storage of carbon from the atmosphere into the deep ocean.

UNESCO: MEDIA SERVICES