3. Which of the following has a nonstandard verb form?

A) Part 1

B) Part 2

C) Part 4

D) Part 6

3. The correct choice is A.

The subject of the sentence is "series," which is singular. The verb, therefore, must be singular, too and needs to be changed to "exists." A correction of Part 1 is shown below in red.

(1) A series of unique ecological communities exist at the bottom of the ocean near thermal vents. (1) A series of unique ecological communities exists 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. (13) This symbiosis is an obviously ancient arrangement that benefits both species.