The Amazon rainforest _______ produces approximately 20% of the world's oxygen _______ spans nine countries.
Which choice completes the text so that it conforms to the conventions of Standard English?
which produces approximately 20% of the world's oxygen
, which produces approximately 20% of the world's oxygen,
—which produces approximately 20% of the world's oxygen
, which produces approximately 20% of the world's oxygen—
Correct Answer: B
Choice B is the best answer. This question tests comma usage with nonessential clauses.
- Context clues: There's only one Amazon rainforest, so the clause is nonessential (additional info).
- Meaning: Nonessential clauses introduced by "which" are set off by commas on both sides.
- Verify: "The Amazon rainforest, which produces approximately 20% of the world's oxygen, spans..." correctly adds extra information.
💡 Strategy: When the subject is already unique or specific, use ", which" with commas for additional information.
Choice A is incorrect because it lacks both commas. Choice C is incorrect because a single dash creates asymmetry. Choice D is incorrect because it mixes comma and dash incorrectly.