To start out I'm going to go back to the thinking about development a little bit, embryonic development, and show you a picture here.
作为这节课的开始，我先稍微回顾一下，一些关于发育过程的内容，先说胚胎发育，这里有张图。
To start out I'm going to go back to the thinking about development a little bit, embryonic development, and show you a picture here.
作为这节课的开始，我先稍微回顾一下，一些关于发育过程的内容，先说胚胎发育，这里有张图。
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