Many young people don’t work hard, and regret it later when the opportunity is gone. They only realize it _______ it is too late.

A．when          B．before         C．in case        D．until

Many young people don’t work hard, and regret it later when the opportunity is gone. They only realize it _______ it is too late.

A. when　　 B. before　　 C. in case　　 D. until