Would it be ______ for you to pick me up at four o’clock and take me to the airport?

A．free

B．useful

C．handy

D．convenient

下列哪项因素可引起支气管平滑肌收缩（）

A.乙酰胆碱

B.普萘洛尔

C.肾上腺素

D.组胺

E.Mg⁺