I think the correct answer is the third statement, electron from escaping from the tube containing the triode. The negative charge on the grid repels any electron in the tube. As a result,the flow of current is controlled. If the field is that strong, all current flow will stop resulting to maintaining the electron cloud in the tube.
To do that, we would need to know what is "described above".
length × width × height
20 cm × 10 cm × 5 cm = 1,000 cm
