1. Which of the following sentences, if added between Parts 12 and 13 of the second paragraph, would be most consistent with the author’s purpose and intended audience?

A) The entire process, of course, sounds thoroughly disgusting and repulsive, but there isn’t anyone that far down to see it.

B) The weight of the trophosome of the Riftia pachyptila is almost entirely due to huge numbers of individual bacterium.

C) These worms, which look like blood-red tulips four to ten feet tall, could not live without their tenants.

D) They are sometimes ten feet tall — imagine how slimy they must be!

1. The correct choice is C.

Only choice C uses a vocabulary and tone consistent to the rest of the passage. Choice A is too personal and judgmental. Choice B is very technical and does not fit the rest of the passage. Choice D is wrong in both mood and tone.

(1) A series of unique ecological communities exist at the bottom of the ocean near thermal vents. (2) Every other community found on the planet is sustained by the sun. (3) But at the bottom of the sea there is no sun. (4) The ocean water, in certain spots where the earth’s plates are joined, is rich in hydrogen sulfide from its interaction with the hot basalt beneath the ocean’s floor. (5 ) Hydrogen sulfide is, of course, a deadly poison to life on the surface. (6) Bacteria in these vents eat the sulfide. (7) With the energy produced by splitting apart the hydrogen sulfide compound, these bacteria produce enormous quantities of starches and sugars much as the plants on the earth’s surface do. (8) With this richness, the bacteria multiply by the billions.

(9) These bacteria are the staff of life around the vents. (10) The smaller animals eat the bacteria, and bigger animals eat the smaller ones, ensuring the food chain. (11) Other creatures live together with and because of the bacteria. (12) The giant worms, for example, provide shelter inside their tubes for the bacteria who, in turn, produce carbohydrates which enter the worm’s blood stream. These worms, which look like blood-red tulips four to ten feet tall, could not live without their tenants. (13) This symbiosis is an obviously ancient arrangement that benefits both species.