知识点 6

Use colons to introduce elaborations (lists, explanations) when grammatically valid.

Use a colon only after a complete clause to introduce a list, explanation, or elaboration.

核心知识

A colon signals "here's what I mean" or "here's the list." The clause before the colon must be grammatically complete on its own—if it isn't, the colon doesn't belong.

深入理解

A colon is a spotlight: it points the reader's attention forward to what comes next. But it has one strict rule—what comes before the colon must be a complete sentence.

Correct:
→ "The researchers identified three key factors: temperature, humidity, and light exposure."
("The researchers identified three key factors" can stand alone.)

→ "The conclusion was clear: further testing was needed."
("The conclusion was clear" can stand alone.)

Incorrect:
→ "The three key factors were: temperature, humidity, and light exposure."
("The three key factors were" is incomplete—"were" needs its complement.)

→ "The study focused on: migration patterns, breeding cycles, and habitat loss."
("The study focused on" ends with a preposition that needs its object.)

On the SAT, wrong answers often place a colon after a verb or preposition that needs its object to complete the thought. The fix is usually to remove the colon entirely and let the sentence flow.

分步讲解

  1. Find the proposed colon location.
  2. Read everything before the colon. Does it form a grammatically complete sentence?
  3. If yes, check what follows—a colon can introduce a list, explanation, or elaboration.
  4. If no (the clause before the colon ends with a verb like 'are' or a preposition like 'of'), the colon is invalid.
  5. Eliminate any answer choice that places a colon after an incomplete clause.

常见误解

  • "A colon can go anywhere before a list." Only if the clause before it is complete. "She bought: eggs, milk, and bread" is wrong because "She bought" needs a direct object to be complete.
  • "Colons and semicolons are interchangeable." They serve completely different functions. A semicolon joins two independent clauses. A colon introduces an elaboration after one complete clause.
  • "You need a colon before every list." Many lists flow naturally from the sentence without any colon: "She bought eggs, milk, and bread."
题目

示例解析

In a report published last spring, marine biologist Dr. Lena Johansson identified three primary threats to coral reef ecosystems in the ______ rising ocean temperatures, increased acidification, and agricultural runoff from coastal development.

Which choice completes the text so that it conforms to the conventions of Standard English?

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