while引导的是表语从句吗

The best time to startthinking about possible careers is whileyou are still at school, before you make any choices about your futureeducation.

请问老师们，while引导的是表语从句吗？

The best time to startthinking about possible careers is while you are still at school, before youmake any choices about your future education.

参考译文：开始考虑你可能的职业生涯的最好机会是在你还在学校的时候，在你对你将来的教育做出任何选择之前。

备注：以上句子主干是：The best time iswhile you are still at school.

备注：以上是while引导表语从句。