在一棵度为3的树中，若有2个度为3的结点，有1个度为2的结点，则有（）个度为0的结点。
A．4
B．5
C．6
D．7
参考答案：C
Children get tired of learning often because they _____ to do better than they can, both at school and at home. [ ]
A. hope
B. are hoped
C. expect
D. are expected
严重缺水并出现酸中毒时，治疗包括
A．解除病因
B．补充血容量
C．纠正酸中毒
D．补充钾盐
