应该用陈述语气：
The opponents acknowledged that they were defeated对手们认输了.
I acknowledge that her criticism is just.我承认她的批评是公正的.
The first step to knowledge is to acknowledge that we are ignorant. 走向知识的第一步是要承认自己的无知.那后面的时态根据什么来定一般根据主句时态决定that从句的时态，时态要一致，即主句是过去式，宾语从句也要用过去式。