回复：先谢大师们，父母绿卡后离开美国有4年了，是什么办法再申请啊？

就是重新从头由我作为公民帮他们申请，跟第一次一样？ 还是有其他的程序要先完成？毕竟他们有曾经绿卡的历史
-They need to give up their green card in a US Consulate, and then apply for the B2 visa to enter US. Then, you can sponsor their green card as you did before. Another choice is that after they give up the green card, you can sponsor their immigration visa application and then they can use the immigration visa to enter US to become the green card holder.