木材的（）是木材物理力学性质是否随含水率而发生变化的转折点。
A．平衡含水率
B．自由含水率
C．化学含水率
D．纤维饱和点
参考答案：D
（）满足了投资者根据不同的风险收益偏好进行交易选择的需求。
A.份额分级
B.交易所上市
C.可分离交易
D.一只基金，多种选择
Has Jack finished his homework yet?
I've no idea, But he _____ it the whole afternoon. [ ]
A. would do
B. was doing
C. did
D. had done
