Rarefaction occurs only in a wave.
a. sympathetic.
b. longitudinal.
c. transverse.
d. forced.

The correct answer to the question is : B) Longitudinal wave.

EXPLANATION:

Before coming into any conclusion, first we have to understand the nature of sound wave.

The sound wave is a longitudinal wave in which the direction of vibration of particles are parallel to the direction of wave propagation.

In this type of wave, one will find compression and rarefaction. Compression is the high pressure region in which the particles are closely aggregated to each other.

Rarefaction is the low pressure region in which the particles are far away from each other. There is large separation between particles as compared to compression.

Hence, the correct answer is sound wave.

b.

explanation:

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.