21 .To climb the mountain is ___ hard work and to go down the mountain is ___ great danger.
A. / ; / B. a;a C. a;/ D. /;a
22. The boss _____ company I worked in two years ago has ______ in solving such a kind of problem.
A. whose; much experience B. who; many experiences
C. whose; many experience D. which; much experience
23. ____________ of the land in that district __________ covered with trees and grass.
A. Two fifith; is B. Two fifith; are C. Two fifths ;is D. Two fifths; are