secondary villus

例句：

1. 1. The doctor examined the patient's secondary villus and found no signs of infection.
   医生检查了患者的次级绒毛，没有发现感染的迹象。
2. 2.During pregnancy, the secondary villus grows to protect the developing fetus.
   在怀孕期间，次级绒毛生长以保护正在发育的胎儿。
3. 3. The study revealed that the secondary villus plays a crucial role in immune response regulation.
   研究发现，次级绒毛在免疫反应调节中起着至关重要的作用。