下列各句中加横线成语的使用，正确的一项是（ ）

Kathy ________ a lot of Chinese when she was working in Beijing during the summer vacation.

_______ you are busy now, let’s go next time, OK

Lily, why are you still here School is over for half an hour.– Because I ______ my task yet. I still need one more hour.

It worried her a bit ____ her hairwas turning grey.