世界职业教育体系发展趋势形成“职业教育——就业——继续教育——更高层次的再就业”良好循环机制。
参考答案：对
---John came to school as early as usual.
---So he did.He comes so early_____ to make the best of time to study.
A．So
B． and
C．but
D．as
测定总锰的水样采集后，为什么要用硝酸酸化至PH<2？
