At night là thì gì

Câu 1 : at night là thì gì ?
Câu 2 : cấu trúc thì của câu hỏi 1 dạng khẳng định.
Câu 3 :
George told Martina that she shouldn't go out alone at night. 
A. George warns Martina about going out alone at night.
B. George didn't want Martina to go out at night.
C. George had warned Martina against going out alone at night
D. George warned Martina about going out alone at night.