Invalid marriage refers to the combination of men and women lacking the conditions for the establishment of marriage. It includes invalid marriages that violate legal conditions and marriages that violate legal procedures. The legal conditions for marriage are: 1. Both men and women must be completely voluntary; 2. Must reach the legal age of marriage; 3. Must it is in line with monogamy. The marriage process is roughly divided into three steps: application, review, and registration.
According to the above definition, which of the followings is invalid marriage?
Xiao Lin and Sanjie were childhood sweethearts, but their parents were very opposed to this marriage, so the two resolutely eloped to live a de facto married life.