Most visitors to the United States will need a visa(签证) as well as a passport and a health record. There are various kinds of visas depending on the estimated length of stay, even more important, on the purpose of your visit. For example, among the types of visas available are: B1-- Normal short visits for business, B2-- Normal short visits for pleasure, Fl-- Student, and F2-- Family of student. A small white form, 1-94, will be attached to your passport showing your classification (类别), arrival date, purpose of visit, and departure date. If you want to stay longer than the date on this form, you must apply to the United States Immigration Service (移民局) for an "Extension of Stay" at least one month before the date indicated. Be sure not to stay beyond the date on which you should leave without an approved extension. The "departure date" on the small white form gives the date ______.
A. to which you can extend your stay B. on which you apply for a longer stay C. on which you arrive in the country D. by which you must leave the country