Bluetooth uses which digital modulation technique to exchange information between paired devices?

A.
PSK (phase-shift keying)

B.
FSK (frequency-shift keying)

C.
ASK (amplitude-shift keying)

D.
QAM (quadrature amplitude modulation)

Explanation:
Phase shift keying is the form of Bluetooth modulation used to enable the higher data rates achievable with
Bluetooth 2 EDR (Enhanced Data Rate). Two forms of PSK are used: π/4 DQPSK, and 8DPSK.
http://www.radio-electronics.com/info/wireless/bluetooth/radio-interface-modulation.php