#Python, 19 15 14 bytes
a.py
00000000 70 72 69 6e 00 28 32 50 69 0a 74 22 41 22 |prin.(2Pi.t"A"|
b.py
00000000 70 72 69 6e 74 22 42 22 00 64 00 00 02 00 |print"B".d....|
c.py
00000000 00 00 00 00 74 0a 70 72 69 6e 74 22 43 22 |....t.print"C"|
I came up with this solution when I noticed that python (2.7.6 on Ubuntu 14.04) after seeing a NUL character will ignore the rest of that line.
Shortened by 1 bytes once I realized that the space after print wasn't needed. And shortened by 4 more bytes once I realized that the NUL character also cause the newline to be ignored so I can use it to break lines in the middle of a keyword.