"Flash marriage" refers to the fact that men and women marry within half a year of love. A research institute has investigated all divorce cases tried by a city court. The results show that the proportion of flash marriage couples suing for divorce within three years is much higher than non-flash marriage couples. The research agency believes that flash marriage is an important reason for the current divorce of couples. Which of the following, if true, would most weaken the above argument? ['Survey finds that couples with the fastest divorce are often not flash couples.', 'Agreement divorce cases handled by the civil affairs department accounted for 70% of the total number of divorce cases in the city.', 'Survey shows that flash marriage couples have more harmonious relationships after marriage.', 'Survey shows that couples who have been in a long relationship have a higher divorce rate than flash marriage couples.']