Which of the following is normally the longest-lived reservoir for carbon? a. atmosperic co2b. marien plankton (primary producers consumers)c. fossil fuelsd. wood

The correct answer is - fossil fuels.

The fossil fuels are by far the longest living reservoir of the carbon. The reason for that is that the fossil fuels have came to be from died out living organisms that had stored carbon in them. Those organisms eventually died, and as they died they were covered with sediments, mud, water, thus the carbon remained trapped in them instead of continuing its path in the carbon cycle. That carbon remained out of touch with the carbon cycle with tens and even hundreds of millions of years while it has slowly been becoming part of the fossil fuels.

Only recently, since the humans started excavating the fossil fuels, that carbon managed to return into the atmosphere and be part of the carbon cycle. If there was no human intervention it was probably going to take further tens or hundreds of million of years for that carbon to be released.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.