Which of the following is NOT included as source of humidity in this passage

A．Nowadays science is learning more and more about the impact humidity has on all of us by using sophisticated measuring devices.
B．Humidity could interfere with television signals.
C．Humidity may warp priceless antiques.
D．Visual disturbances may decrease in days of low humidity.

A．So it can be reached any time.
B．It is so designed mechanically.
C．So it can prevent moisture.
D．The piano needs to be tuned frequently.