After checking the report ,（ ）.
A、several mistakes were discovered
B、several mistakes are discovered
C、the manager discovered several mistakes
D、the manager will discover several mistakes
【正确答案】：C
【题目解析】：根据前半句的checking可知后半句的主语要与check是主动关系，故可排除选项A和B；after意为“在......之后“，所以要用一般过去时，故选C。