The correct answer would be - pupils expand or become bigger so more light can enter the eyes.
Explanation:
When Arun crosses the playground he was in a warm and sunny condition where light is more than required so the pupil becomes small in an excess light condition.
So, that less light can enter the eyes and when he enters into a dark auditorium then less light enters in his eye and he can't see a thing and pupil expands and more light enters the eye enabling to see and able to make out the way between the rows of seats