I'm pretty sure your answer is VPN. Hope this helps!
I don't see any error on your code, everything is well written and simple. Except trying putting PUBLIC on your Class displayer. If you encounter the same problem again try to rebuild your whole code and try to recompile the whole code. Even try restarting your personal computer.
Answer:
A <b>
Normally AD and BC are written in bold letters.
for example : The terms anno Domini (AD) and before Christ (BC).
Within available option the best option to choose is <b> hope it helped