订立经济合同必须遵守法律法规，还必须遵循（）；（）的原则。
参考答案：平等自愿、诚实信用
Peter has been busy these days and seldom ____ to come over to have a chat with me.
A．does he have time
B．he has time
C．doesn’t he have time
D．he hasn’t time
将60℃的硫酸铜饱和溶液100克，冷却到20℃，下列说法正确的是[ ]
A．溶液质量不变
B．溶剂质量发生变化
C．溶液为饱和溶液，浓度不变
D．有晶体析出，溶剂质量不变
