A customary adoption is an adoption created by operation of custom, i.e. — a common law adoption. See e.g. Matter of Nq, 14 I. N. Dec. 135 (BIA 1972); Matter of Poon, 14 I. N. Dec. 155 (BIA 1972). Section 1153(a)(2) gives second preference status to unmarried sons and daughters of lawful permanent residents for the issuance of immigrant visas.