"The key to______the medical problems at the root is health care reform," said the minister.
【正确答案】 B
【答案解析】the key to doing sth．意为“做……的关键”，其中to为介词，其后一般接名词或动名词，所以排除选项A、D。因the key与solve为逻辑上的主谓关系，所以应用动名词的主动语态。故选B。