In the kirby-bauer disk diffusion test, the of the zone of inhibition is measured and used for interpretation.
diameter
microbial population
circumference
depth

The correct option is : a. diameter    

Explanation:

The Kirby–Bauer test or the disk diffusion test, is a method to determine the antibiotic sensitivity of the given bacteria. This test involves the use of antibiotic discs to determine the effect of antibiotics on the bacteria.

In this test, the wafers having antibiotics and the bacteria are placed on the agar plate and incubated. If the antibiotics present stops the growth of the bacteria, there will be an area around wafer with no bacterial growth, such an area is known as the zone of inhibition.

The diameter of this zone of inhibition is measured to determine the antibiotic sensitivity of the given bacteria.

a. by using fur or clothes to trap heat energy near the body