$64,000 question
noun [ C usually singular ] uk/ˌsɪk.sti.fɔː ˌθaʊ.zəndˌdɒl.ə ˈkwes.tʃən/ us/ˌsɪk.sti.fɔːrˌθaʊ.zəndˌdɑː.lɚ ˈkwes.tʃən/ (also million-dollar question)
事关重大的问题;难题
an important or difficult question on which a lot depends
The $64,000 question is, can we repeat last year's success? 关键问题是，我们能再创去年那样辉煌的成绩吗?