I‘ve worked here since I__________ Harvard Business School.
A、leave
B、left
C、have left
D、had left
Without the help of people from every corner of the world, people in Wenchuan County, Sichuan Province__________recovered very quickly from the May Twelfth Earthquake.
A、must not have
B、couldn‘t have
C、may not have
D、can‘t have
Dinosaur scientists can probably know whether dinosaurs were good parents by __________ .