—How should we deal with air pollution?  

—It will be very difficult _____ there are fewer factories and cars.[ ]

A. until

B. unless

C. if

D. after

对下表中国古代两大选官制度的信息解读正确的是（）

A.察举制强调官员的才能第一

B.科举制注重考察自然科学

C.察举制容易导致任人唯亲

D.科举制不利于统治基础扩大