You should never base anything on a theory that _________ impractical in practice.
A. is proved B. prove C. proves D. proved
With my hand-held Reader, I’ve read more books in the past six months than I ________ in the past six years.
A. doing B. did C. have D. do
Since then, more than 2 billion apps have been downloaded at prices ________ free to $900.
A. ranging between B. ranging from C. rang between D. rang from
My arrival was timed perfectly; it was the second weekend of November, when the world largest wine auction ________.
A. held B. was being held C. was held D. was to hold
When McKie brings friends or volunteers to the area where she works, most of ________ spend the first day sobbing.
A. them B. whom C. that D. which
_______ in the 1800s and first mass-produced in Germany, the harmonica(口琴) was designed to play simple folk tunes.
A. Being invented B. Inventing C. Invented D. Having invented
