Express yourself!

Can you guess which expression is best used in these situations?

someone is arriving:

You havent seen someone in a very long time...What do you say?

a. Nice to meet you.
b. Have a nice trip
c. Long time no see!

someone is leaving:

You are seeing you friend off at the airport...What do you say?

a. Welcome back!
b. Have a nice trip!
c. Congratulations!

encouragement:

Someone has a big test tomorrow...What do you say?

a. Good luck!
b. Keep up the good work!
c. Come in.