一个主句中不可以有两个谓语动词,若选C 则found和is同为动词,这是双谓语的错误.而且find it impossible to do sth是固定短语
另外,宾语从句的that不可省略,所以如果一定要用is 那应该将其转化为宾语从句的形式he found that it is impossible to get there on time.