The correct answer is (d) Crystal oscillators
The explanation is: The sawtooth generator generates an output resembling the teeth of a plain toothed saw. A blocking oscillator is a free running generator, used to produce narrow trigger pulses. A multivibrator is used to produce an output varying between 2 states- a high and low, producing square waves of a different duty cycle. A crystal oscillator is the only one of all used to produce sinusoidal signals.