单选题 The integer n is a multiple of both 5 and 3. Which of the following is (are) true?
I. n is odd.
II. n=30.
III. n is a multiple of 15.
  • (A) III only
  • (B) I and II only
  • (C) I and III only
  • (D) II and III only
  • (E) I, II, and III


【正确答案】 A
【答案解析】To answer this question, take each of the Roman numerals independently and eliminate answer choices as follows:
Roman numeral I: For n to be a multiple of 5 and 3, it must also be a multiple of 15.15×2=30, which is an even number. Roman numeral I is not always true, so eliminate answer choices B, C, and E.
Roman numeral II: 15, 45, 60, etc., are also multiples of 5 and 3; therefore, Roman numeral II is not always true. Eliminate answer choice D.
Roman numeral III: Because 3×5=15, n will also be a multiple of 15. Roman numeral III is always true, and the correct answer choice must be A.