Answer:
A hand held up at chest height, then slowly lowered to waist height
Explanation:
For answering this question, it is best to try to do the described gestures by yourself in order to visualize them and compare with the given situation. The situation is that choir and orchestra are finishing the song and the volume is decreasing (going down) to the lowest tones. So when we compare all the given gestures with this, we notice that only the third one includes lowering of the hand which represents the lowering of the volume. Gestures often follow the very essence of the action. Some of them are a product of social agreements like clapping at the end of the performance ( Two hands brought together with a clap in front of the chest).
