英语 In some countries there are already a number of firms ______ c_英语解答

英语 In some countries there are already a number of firms ______ computer programming.
A.specialized in
B.specialize in
C.specializing in
D.specializes in
为什么

人气：190 ℃　时间：2020-01-30 09:26:03

解答

C.因为前面有一个there be句型,且不为被动语态,紧跟其后的动词用ing形式