The gap between rural and urban education in China is widening and education is the key t

问题补充：

The gap between rural and urban education in China is widening, and education is the key to rural problems.

A. solving

B. solve

C. have solved

D. having solved

答案：

(答案→)A. solving

B. solve

C. have solved

D. having solved

解析：考查非谓语动词。the key to……的关键，to为介词，故选A。