She _____ her hometown since she was 18 years old. She told me she would return soon.
A：has left
B：has been away from
C：left
D：went away
硝化细菌通过化能合成作用形成有机物，需要下列哪种环境条件？（ ）
Jim______ sing Chinese songs very well now, but he______do it last year.
软流层位于（）
