下列叙述中，金属a的活泼性肯定比金属b的活泼性强的是 (       ) 

A．a原子的最外层电子数比B原子的最外层电子数少

B．a原子电子层数比b原子的电子层数多

C．1mol a 从酸中置换H⁺生成的H₂比b从酸中置换H⁺生成的H₂ 要容易

D．常温时，b能从水中置换出氢，而a不能

He noticed that Joan was studying him closely, but her expression gave away nothing of what she was thinking.

A．revealed

B．disposed

C．reminded

D．distributed