分母是8的所有最简真分数的和是[ ]
A.1
B.3
C.2
答案:C
22.If you keep practising your son in football, he________ to make a famous player.
A.wants
B.hopes
C.promises
D.Wishes
关于食管的分化和发育哪些是正确的?()
A.食管上皮来自前肠内胚层
B.管壁的结缔组织来自脏壁中胚层
C.食管腺由内胚层分化而来
D.肌层来源于体节的生肌节
E.外膜由外胚层形成