A:That; very
B:That; quite
C:What; very
D:What; quite
用化学用语填空:(1)三个氢原子____
(2)两个五氧化二氮分子____(3)3个氢氧根离子____
(4)氧化镁中镁元素为+2价____
东北地区发展农业的主要制约因素是 ( )
关节活动起来非常灵活,与之有关的结构特点是关节结构里有( )