period of yolk formation

例句：

1. 1.The period of yolk formation is crucial for the development of the embryo.
   卵黄形成期对胚胎的发展至关重要。
2. 2.During this period, the egg membranes will gradually close, forming the yolk sac.
   在此期间，蛋膜将逐渐闭合，形成蛋黄囊。
3. 3. The study of the period of yolk formation has important implications for understanding the development of the human fetus.
   研究卵黄形成期对于理解人类胎儿发育具有重要意义。