If a migrant worker is undocumented, it could mean that he or she isn't legally allowed to be working on the farm.上面If a migrant worker is undocumented是真实条件句。?it could mean that he or she isn't legally allowed to be working on the farm 是主句，这里的?could 意思是“可能”，是表示推测意思，可以表示现在或者将来可能性。不可以看做属于第一条件句，因为这里只有一个条件状语从句，没有第二、第三个条件句。