21.Jumping out of ______ airplane at ten thousand feet is quit ____ exciting experience.
A. \; the B. \;an C. an; an D. the; the
22.They asked me so many ______ questions that I got ______.
A. confusing; confusing B. confused; confusing
C. confused; confused D. confusing; confused
23. Once ______ , the plan can’t be changed.
A. begin B. beginning C. began D. begun
24. He observed a stranger _______ around the store at 12 p.m. last night.
A. to hang B. hang C. hanging D. to be hanging
