1. Learning experience happens to us ________ our lives.
A．on B．in C．across D．throughout
2. Going on a trip into ________ space must be quite ________ exciting experience.
A. /；the B. the; the C. the; an D. /；an
3. —May I smoke here?
—If you _______ , choose a seat in the smoking section.
A. must B. should C. may D. can
