Using gcc on multiple file objects

In an exam I took I found myself in front of this question:

What's the result following this command?

gcc file1.o file2.o file3.o

A)Nothing, it's using the wrong syntax

B)Links the file objects but won't produce any result unless specified an output

C)An executable file a.out

I thought it was A) the wrong syntax, but I was wrong, could you guys help me figure out which is the correct answer? (I suspect the third one, but I also know that gcc won't always create an executable if ran)

p.s.If you could give me a thorough explanation I would be very greatful