The disturbance that occurs as longitudional waves travel through a medium can be described as a series of?
a. oscillations and refractions
b. destructions and constructions
c. propagrations and compressions
d. rarefactions and compressions

There are three  types of waves which are named as -

1-Longitudinal wave

2-Transverse wave

3-Matter wave.

Here we will consider only transverse  and longitudinal waves.

A transverse wave is that  type of wave in which the direction of propagation of wave is perpendicular to the direction of vibration of particles.It moves in the form of crests and troughs. The waves like water wave, the waves in a stretched  string fixed at two ends with rigid walls.

A longitudinal wave is a mechanical wave in which the oscillation of particle is parallel to the direction of propagation of the wave. In a longitudinal wave,some part  of the medium  has high pressure where the particles of the medium are compressed which is followed by low pressure regions where particles are  largely separated as compared to high pressure zone.

The high pressure zone is called Compressions and low pressure zone is called Rarefactions. The compressions and rarefactions are repeated gradually through out the medium for which the wave is propagated from one point to another point in that specific medium. One may take an example of sound wave.

Hence  the option D  is the correct answer.

well clustered together.

points close on a scatter diagram

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =