A family made a $$100\text{km}$$ trip. For half the distance, they drove at $$50\text{km}$$~ per hour; for the other half, they drove at $$25\text{km}$$~ per hour How many hours did this trip take? 
选项为:A:$$3$$  B:$$4$$  C:$$5$$  D:$$6$$  请回答其中一个选项.