Which of the following statements explains why the earth has a gravitational field? a. it has mass. b. it has an electric charge. c. it is revolving around the sun. d. it is rotating on its axis.

The case of the gravity force between 2 bodies is according to Newton's law for gravity

Then, the gravitational field of the earth is cased by the mass of the earth.

The electric charge cased the electric field around the earth according to Coulomb's law.

The revolving around the sun and the rotation on its axis save the earth on its orbit around the sun and cased the 4 seasons change and the day-night change.

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 =