在细胞壁各层中，木素总含量主要分布在次生壁中。
参考答案：对
It’s ________ unusual chance for Mr White to get such ________ useful advice.
A．an; /
B．a; an
C．a; the
D．an; an
The new movie ________ to be one of the biggest moneymakers of all time.[ ]
A. pretends
B. agrees
C. promises
D. declines
