We can give you a lift to the airport _______ you don’t mind the crowdedness, for there have already been four of us in the car.

A．unless

B．though

C．provided

D．until

只用一种试剂就能方便地区分稀盐酸、食盐溶液、澄清石灰水，这种试剂是（    ）

A．无色酚酞试液

B．石蕊试液

C．二氧化碳

D．氢氧化钠溶液