恒流吸气的气道压曲线特征为上升支呈（）。

A.斜直线形

B.抛物线形

C.指函数曲线形

D.正弦波形

E.S形曲线

At the end of the meeting, it was announced that an agreement ________.

A．has been reached

B．had been reached

C．has reached

D．had reached