The grid in a high-vacuum triode is usually kept negatively charged with respect to the cathode so that

the electrons may be

A. accelerated toward the cathode.

B. attracted to the anode instead of the grid.

C. attracted to the cathode instead of the grid.

D. accelerated toward the anode.

The grid in a vacuum triode is usually kept negatively charged

with respect to the cathode so that the electrons may be

attracted to the anode instead of the grid. (B).

I'm pretty sure that nobody in your high school physics class

has ever seen a vacuum triode, or has ever used anything that

had vacuum triodes inside, or has the slightest idea of what a

vacuum triode is, or will ever need to know what a vacuum triode

is, or would realize any material benefit, now or in the future, from

that knowledge. And I'd be very surprised if your time in high school

physics is being wasted to teach it to you.

Vacuum triodes were essential in virtually ALL electronic

equipment when I was in high school, but even then, it wasn't

taught until college. I happened to learn about them on my own

while I was in high school, because that was when I got my

amateur radio ("ham") operator's license.

So how did you happen to run into this question?