在这些实验和实地观测的基础上，人们制定了所谓的竞争排斥定律，根据该定律，没有两个物种可以占据相同的生态龛。
On the basis of these experiments and of field observations, the so-called law of competitive exclusion was formulated, according to which no two species can occupy the same niche.
在西安市选取了数十条人行横道进行实地观测。
Field observations were carried out at dozens of crosswalks in Xi an.
听完解说后我们来到户外实地观测，天空已经变暗了。
After hearing the briefing, we walked outside to watch the eclipse. The sky had already become dimmer.
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