21) ____ on a clear day,far from the city crowds,the mountains give him a sense of infinite peace.

21) ____ on a clear day,far from the city crowds,the mountains give him a sense of infinite peace.
A) If walking B) While walking C) Walking D) When one is walking
22) I understood you were third-year students ____ in English.
A) who majors B) who major is C) have majored D) majoring
23) A cool rain was falling,____ with snow.
A) mixed B) mixing C) to mix D) having mixed
24) ____ by the police,the kidnappers had no choice but to surrender.
A) Surrounded B) Surrounding C)having surrounded D) To be surrounded
25)____ equal educational opportunities,American Indians in the reservations remained backward and illiterate for a long time.
A) Deprived off B) Depriving off C) Deprived of D) Depriving of