I believe the answer is letter B. I think this because the trumpet only requires the use of three fingers, so it may be easier to play than woodwind instruments.
To make a sound, kids blow air through almost closed lips. That can help strengthen the fine motor skills of the mouth.
The child needs to be able to breathe strongly and with control, in and out, using diaphragm muscles. Doing this will develop the motor skills they would later on need.
Hope this helped you!