在稳定的DNA双螺旋中，哪两种力在维系分子立体结构方面起主要作用
参考答案：在稳定的DNA双螺旋中，碱基堆积力和碱基配对氢键在维系分子立体结构方面起主要作用。
当伸肘时，肱二头肌、肱三头肌如何运动
A．肱二头肌收缩，肱三头肌舒张
B．肱三头肌收缩，肱二头肌舒张
C．肱三头肌收缩，肱二头肌收缩
D．肱二头肌舒张，肱三头肌舒张
Jack describe his father, who____ a brave boy many years ago, as a strong-willed man.
A．would be
B．would have been
C．must be
D．must have been
