Two kittens are sleeping in a sunny spot. they are relying mainly on what kind of heat transfer?

Radiation

Explanation:

They are relying majorly on radiation. Radiation as a mode of heat transfer is the transfer of heat energy from one body to another without any intervening medium between the source of heat and the body. Without intervening medium means that radiation does not requires material medium for its propagation and it occurs mainly in vacuum.

Example of radiation is the source of heat directly from the sun. Since the kittens are sleeping in a sunny spot, therefore they get their heat through radiation.

it is a negative acceleration

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 =