How Composition relation be developed beween Student Course.

I am working with two classes student and courses in a c# programming language (console application )I am confused in the context of what could be a type of relation ship between these two classes … either composition or aggregation…?both of them are dependent on each other but problem rising in a life time of objects …each student can take 3 to 7 courses in my logic life time of instances are different… here a problem..
ONE object(instance) contains multiple instances....