Many media have said that there is a serious imbalance in the ratio of men to women in China. By 2020, the number of men in China at marriage will be 30 to 40 million more than women, which means that one in five men will not find a spouse. Tens of millions of men have no wives to marry. The one that best supports the above argument? ['Popularization of gender selection technologies.', 'The census has been very successful.', 'Late marriage and late childbirth are common.', 'Increased celibacy.']