下列选项中，（）不是柱切技术的主要作用。
A、改善分离效果
B、保护平衡柱
C、缩短分析时间
D、改变组分流径
参考答案：B
Our plan is to plant 50 trees. And we have planted half of them .
A．the other day
B．yet
C．so far
D．in the past
The library from __________we borrow books will be rebuilt next year.
A．that
B．which
C．where
D．whom
