lf the internal energy of the system decrease, then what can be conclude about the heat and the work done? A, Heat is added to the system and work is done by the system B, Heat is removed from the system and work is done by the system C, Heat is removed from the system and work is done on the system D, Heat is added to the system and work is done on the system​

Your answer should be B.

If your internal energy or heat of a system decreases then you know that you are taking that energy out and doing work.

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 =