After the interview? It's too late to answer the interview question. Better learn the whole
System.IO
. And, pretty much all of BCL and some other parts of FCL. Well, I cannot guarantee they will ask it all at your next interviews, but I'm pretty much sure, the next questions will be very different. :-)
And the interview preparations is the useless activity. Please read this:
SSRS interview questions and answers[
^].
—SA