参考答案

正确答案：A
解析：根据题干中的信息词extramarital affair定位到Commitment标题下第三句"For strong families’ commitment and sexual fidelity are so closely linked that an extramarital affair is regarded as the ultimate threat to a marriage(婚外恋被看作是对婚姻的最大威胁，因为责任心与忠诚是与幸福家庭紧密相连的) ”，题干表述正确。