1974 AMC 12 第 13 题
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所有题目均经美国数学协会（MAA）官方合法授权使用。
13.
以下哪一项与“若 为真，则 为假”等价？
Which of the following is equivalent to “If is true then is false”?
“ 为真，或 为假。”
“ is true or is false.”
“若 为假，则 为真。”
“If is false then is true.”
“若 为假，则 为真。”
“If is false then is true.”
“若 为真，则 为假。”
“If is true then is false.”
“若 为真，则 为真。”
“If is true then is true.”
答案：D
小提示：
一个命题与其逆否命题等价
An implication is equivalent to its contrapositive
大提示：
将蕴含方向反转，并分别否定“ 为真”和“ 为假”
Reverse the implication and negate both “ true” and “ false”
解答：
“ 为真蕴含 为假”的逆否命题是“ 不为假蕴含 不为真”。这正是“若 为真，则 为假”。
因此，正确答案是 D。
The contrapositive of “ true implies false” is “ not false implies not true.” This is exactly “If is true then is false.”
Therefore, the correct answer is D.
其他年份的第 13 题
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