食管癌的典型症状是
A．咽下疼痛
B．食管内异物感
C．胸骨后烧灼感
D．进行性咽下困难
E．呕吐粘液
参考答案：D
We saw many students playing on the playground, most of them _____ girls.
A．are
B．being
C．were
D．have been
中心软件SIC存放配置文件的目录名是（）
A.install SIC%/data
B.install SIC%/update
C.install SIC%/queue
D.install SIC%/conf
