PSAT Writing and Language Question 309: Answer and Explanation

Question: 309

• A. NO CHANGE
• B. life, from microscopic phytoplankton and tiny krill at the bottom of the food chain to killer whales and leopard seals at the top; giving
• C. life; from microscopic phytoplankton and tiny krill at the bottom of the food chain to killer whales and leopard seals at the top—giving
• D. life, from microscopic phytoplankton and tiny krill at the bottom of the food chain to killer whales and leopard seals at the top, giving

Correct Answer: D

Explanation:

Difficulty: Hard

Category: Sentence Structure: Commas, Dashes, and Colons

Getting to the Answer: You must determine what punctuation is correct around this long phrase that appears in the middle of a sentence. As written, the descriptive phrase that begins "giving these waters" confusingly runs into the previous part of the sentence, so eliminate (A). The underlined prepositional phrases are best viewed as parenthetical information that describes the type of life in Antarctic seas. If the phrases were removed, the sentence would still stand on its own: "Antarctic seas teem with life,... giving these waters a vital status among the Earth's ecosystems." Look for an answer choice that punctuates the parenthetical information appropriately, using either a pair of commas or dashes to set off the nonessential phrase. (D) does this with commas and is correct. (B) and (C) are incorrect because the use of a semicolon would indicate that two independent clauses are being joined, but each creates one dependent clause.