矿质元素可根据其在食品中的含量细分为常量元素、微量元素和超微量元素，下述这些元素中属于微量元素的是（）
A、钠
B、磷
C、铝
D、铁
参考答案：D
唐后期藩镇割据指的是（）后以河北、山东、河南各地节度使为代表的拥兵自重、对抗中央的军阀割据势力。
If human beings had been a bit less greedy and cruel, more birds and animals _______dying out.
A．ought to avoid
B．could have been avoided
C．should have avoided
D．might have avoided
