Suppose there are two women, A and B, who use A's egg cells and Du Yuanhe's sperm to make in vitro fertilization, and then implant the fertilized eggs into B's body. B then marries Zhang Bingkuan. In this case, the biological father of the child is Du Yuanhe, and the legal father is Zhang Bingkuan. Similarly, Zhang Bingkuan's sperm combines with B's egg cell, and then the fertilized egg is implanted into A's body. A then marries Du Yuanhe, and the biological and legal father of this child is exactly the opposite of the previous one. In this way, these two children have two parents and can establish a legal relationship with any one of them.