1.The unmarried son may leave for stretches of city work, but he is bound to return.
未婚儿子可以去城市打短工,但他一定要回来。
2.The unmarried son or daughter (21 years or older) of a permanent resident
永久性居民的未婚儿女(不小于21岁)
3.An unmarried son or daughter (21 years or older) of a U. S. citizen
美国公民的未婚儿子或女儿(不小于21岁)