According to the Law of Conservation of Matter, the total amount of carbon on Earth. A. increase due to burning of fossil fuels.
B. changes according to the season of the year.
C. always stays the same. D. is decreased by photosynthesis

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 =

snell's law

refractve index = sin incidence / sin refraction