If Adam and Eve are the first humans, and they had two sons Cain as Abel, where did Cains wife come from?

So the Bible mentions two sons of Adam, Why? because they played a part in a needed story.. The recording of the first sacrafices made to God and the recording of the first murder committed..

Just because the Bible did not name other children of Adam and eve does not mean they did not exist.. Adam and eve had centuries of time to have many many Children.. and Cain partnered with one of them..