15. Three quarters of the land here _____ wet land, an ideal place for migrating birds.

A．are

B．is

C．have been

D．Being

关于胎儿发育，正确的是()

A．妊娠8周末胚胎初具人形

B．妊娠10周前称胚胎

C．妊娠10周末胎儿外生殖器已发育

D．妊娠12周以后称胎儿

E．妊娠20周末胎儿内脏器官已发育齐全