Explanation:

• The Theremin is an electronic musical instrument controlled without physical contact by the thereminist (performer).
• The instrument was invented in 1920.
• It is named after its inventor, Leon Theremin, who patented the device in 1928.
• The instrument's controlling section usually consists of two metal antennas that sense the relative position of the thereminist's hands and control oscillators for frequency with one hand, and amplitude (volume) with the other.
• The electric signals from the theremin are amplified and sent to a loudspeaker.

Hence option 4th is correct.