锁骨上淋巴结转移癌的原发部位最常见于（）。
A.甲状腺
B.食管
C.乳腺
D.胃
E.肝
参考答案：D
It's _____ problem _____ we can't work it out.[ ]
A. so confused a; that
B. such a confusing; that
C. such confusing a; so that
D. so a confused; so that
有利于铁吸收的因素是()
A．维生素C
B．磷酸盐
C．草酸
D．植酸
