胸部侧位片肺门区不显影的是（）
A.两上叶支气管
B.右上肺静脉干
C.左肺动脉弓
D.左下肺动脉
E.左上肺静脉干
参考答案：E
My parents have promised to come to see me before I _________ for Africa.[ ]
A. have left
B. leave
C. left
D. will leave
决定一个人身高、肤色等的是[ ]
A．细胞核
B．DNA
C．基因
D．染色体
