Which is the best example of an isolated system? an electric kitchen appliance, such as a dishwasher or refrigerator
a natural body of water, such as a lake or river
a pendulum in motion inside a sealed, empty room
a frog egg that develops into a tadpole, and then an adult frog

The best example would be a pendulum inside a sealed empty room.

Explanation:

i think if it were me i whould divide 300 dide 15

step-by-step explanation:

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 =