ANS:C - trigger section

This is what I understood, don't know if it is correct. If wrong please correct me. !

Trigger section controls the start event of the sweep (ie. Horizontal time base). So this trigger (eg:edge trigger can happen) will happen for each time intervals in most of the oscillators automatically. This will eliminate distortion of signal and a stable display can be achieved.

But one more option is there external trigger which we used in our electronics lab. We will connect external probe to one input of the oscilloscope and we can trigger the input till the display is stable.