Answer:
I am the greatest teacher out of them all, but alas in the end I kill my pupils.
What relies on columns but isn't a house, and asks for help but can't speak itself?
They are many and one, they wave and they drum, Used to cover a state, they go with you everywhere.
What type of bar gets you wet walking in and out of it but keeps you dry inside?
Who makes it, has no need of it. Who buys it, has no use for it. Who uses it can neither see nor feel it. What is it?
If itβs information you seek, come and see me. If itβs pairs of letters you need, I have consecutively three. What am I?