A:具有男尊女卑的思想
B:固定传统的家庭等级观念
C:具有浓厚的宗法观念
D:遵循长幼有序的婚姻礼俗
They ________ carefully, but they didn't ________ anything.
图示“观察小鱼尾鳍内血液的流动”实验及显微镜下观察到的物像,以下哪项解释合理( )