可以单独用的。例子：Have you finished the task?–Not yet.“not yet”意思是：还没有，还没，还没能完成某事，一般用于对完成时的回答。例句：The cause of the fire is not yet known.火灾的原因尚不清楚。
not yet的例句
The product is not yet commercially available.
这种产品还没有上市。
The house is not yet connected to the mains.
这房子还没有通水电。
Details of the government report have not yet been made public.
政府报告的细节尚未公布。
The news is not yet official.
这消息尚未经官方证实。
The new drug has not yet been licensed in the US.
这种新药尚未在美国获得许可。