早期食管癌的临床表现是（）
A.咽下食物哽噎感
B.锁骨上淋巴结转移
C.持续胸背痛
D.吞咽困难
E.声音嘶哑
参考答案：A
用科学记数表示：（1）691000=______，（2）0.00000047=______，（3）-321400=______．
— David, look at the man in white over there. Can you tell me _____?
— He is a doctor. [ ]
A. Who is he
B. who he is
C. what is he
D. what he is
