Answer:
d. All of the above .
Explanation:
The sensitivity of microphone will be more if even feeble sound can create greater vibration in diaphragm . Naturally it is possible if diaphragm is light and can move easily . The movement it it is controlled by current in the coil which makes it electromagnet . All factors that increase the strength of magnet like increasing the no of turns , or a strong magnet will increase the sensitivity.