A gymnast performs an amazing flip! He lands on the floor and his feet put a force downwards on the floor. Newton’s Third Law reaction force is: (A)The weight of gravity on the gymnast
(B)The weight of gravity on the floor
(C)The force of the floor upwards on his feet
(D)The force of the floor downwards on his feet

multiple

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 =