The correct answer is: A. GFSK
GFSK (Gaussian Frequency-Shift Keying) is a modulation scheme that uses a Gaussian pulse to modulate the frequency of a carrier signal. It is a relatively simple and robust modulation scheme that is well-suited for use in Bluetooth systems.
DQPSK (Differential Quadrature Phase-Shift Keying) is a modulation scheme that uses two phase states to represent two symbols. It is a more complex modulation scheme than GFSK, but it offers better performance in terms of data rate and error correction.
BPSK (Binary Phase-Shift Keying) is a modulation scheme that uses two phase states to represent two symbols. It is a simpler modulation scheme than DQPSK, but it offers lower performance in terms of data rate and error correction.
MSK (Minimum-Shift Keying) is a modulation scheme that is similar to GFSK, but it uses a raised cosine pulse instead of a Gaussian pulse. This results in a more efficient use of the available bandwidth, but it also makes the modulation scheme more susceptible to noise.
In conclusion, GFSK is the modulation scheme that is used by Bluetooth. It is a relatively simple and robust modulation scheme that is well-suited for use in Bluetooth systems.