Not all life depends on energy from sunlight. Microbial life has been found in bedrock more than five kilometers below the surface of the Earth, and bacteria have been found on the deep ocean floor feeding on hydrogen and other gases rising from the interior of the Earth through vents in the ocean floor.

The statements above, if true, best support which of the following as a conclusion?

(A) The location in the bedrock where microbial life was found was not near a system of volcanic vents through which hydrogen and other gases rose from the interior earth.
(B) Bacteria are able to exist at the molten center of the Earth.
(C) A thorough survey of a planet's surface is insufficient to establish beyond a doubt that the planet contains no life.
(D) Life probably exists on Sun-orbiting comets, which are cold agglomerations of space dust and frozen gases.
(E) Finding bacterial remains in coal and oil would establish that the bacteria had been feeding on substances that had been produced from energy of sunlight.


The correct answer is (D). My question is - Choice (C) looks a little extreme due to the usage of 'insufficient', specially when 'Survey' was not all mentioned anywhere in the paragraph.

Please help!!

GMAT 2007

GMAT 2007,

The correct answer choice to an inference/draw a conclusion question must be directly supported by evidence from the text. In this case, answer choice D is not the correct answer, as it is an extrapolation outside the scope of the argument rather than a fact directly supported by evidence from the text. Conversely, answer choice C, the best answer is directly supported by the text.

If you are uncertain whether a particular answer choice is directly supported by evidence from the text, place the phrase "it is true that..." before the answer choice. If this choice is inarguably true it will most likely be the best answer.

-dan