Theywereatworkwhentheyreceived_______SOSfrom_______

They were at work when they received _______SOS from _______school, and they immediately stared their police cars.

A. the, the

B. a, a

C. an, a

D. the, a

正确答案：C
参考译文：当他们在工作时接到了来自一所学校的求助于是他们赶紧发动了警车两空均为泛指“S”元音开头前应用an