Steps:
Find the Argument
Find supporting evidence in the text, this is needed before we analyse our possible answers.
Eliminate easy options
These will be the answers that are opposite to what you want (ex. Strengthen instead of weakening)
Determine which answer strengthens or weakens the argument THE MOST
A The carbon that is present on the Earth could have arrived at a later date from an asteroid.
The passage is trying to explain why the Earth has less carbon than expected for a planet that is able to support life. Therefore this option, A, does not strengthen the argument because it is not explaining the lower levels of carbon but rather is saying the carbon could have come from somewhere else (which is irrelevant to us). Therefore A is incorrect.
B The abundance of carbon in the asteroid belt surrounding the inner planets increases the further away you get from the Sun.
The author says ‘there would have been fewer of these oxygen atoms further away from the sun’. The passage is saying that a potential cause for Earth having less carbon than anticipated is because ‘Hot oxygen atoms would have readily combined with carbon, burning to produce carbon dioxide’. Now the final thing we need to understand is that statement B is saying that there is increasing amounts of carbon in the asteroid belts as you get further away from the sun. As we move further from the sun, there is a temperature drop, meaning that there are less hot oxygen atoms readily available to combine with the carbon molecules to form CO2. This would explain why Earth has a lower amount of carbon than other planets in the solar system; because it is closer to the sun and therefore more hot oxygen atoms were able to form CO2 with carbon. This strengthens the argument by supporting a theory that explains why the Earth has less carbon than expected. Therefore B is correct.
C There is no theoretical reason why life has to be carbon based.
This is a distractor option. The author is saying that it is surprising that the amount of carbon for a planet like Earth, that supports life, is lower than expected. Then the author tries to explain why. Option C does not strengthen the argument because it diminishes the need for an explanation of Earth’s carbon levels. If life did not have a theoretical reason for carbon-based life, then it would not matter if the Earth had less carbon than expected. Therefore C is incorrect.
D There are other solar systems with Earthlike planets that have an abundance of carbon on them.
This is another answer that does not strengthen the argument because it does not help explain WHY Earth has less carbon than other planets able to support life in the solar system. Therefore D is incorrect.
E At temperatures that are high enough for carbon to boil away, oxygen would also have boiled away.
This is referring to an old conclusion. The author said this is what was thought to have been believed in the past, but now there is new evidence that carbon is combining with oxygen. Therefore E is also incorrect.