在TCP/IP参考模型中，提供可靠的端到端服务的层次是（）
A.会话层
B.表示层
C.互联层
D.传输层
参考答案：D
—The weather is not good enough for an outing， is it？
—Not in the least. We have not have ______ at this time of the year.
A．a worse day
B．a nicer day
C．such a bad day
D．so fine a day
坡口的形式有几种？
