Except as provided in subsection (b) and subsection (c) no immigrant shall be admitted into the United States unless at the time of application for admission he (1) has a valid unexpired immigrant visa or was born subsequent to the issuance of such visa of the accompanying parent, and (2) presents a valid unexpired passport or other suitable travel document, or document of identity and nationality, if such document is required under the regulations issued by the Attorney General. With respect to immigrants to be admitted under quotas of quota areas prior to June 30, 1968, no immigrant visa shall be deemed valid unless the immigrant is properly chargeable to the quota area under the quota of which the visa is issued.