21. The milkman ________ the spotted cow, from among a herd of two hundred. 

A. separated    B. held    C. elected              D. selected

22. You’d better put on more clothes. It’s ________ cold upon high mountaintops.

A. frozen                      B. freezing    

C. freeze                      D. to freeze 

23. But if a treatment ________ delayed the disease by seven years were to be available, the number of sufferers would drop by 40% by the middle of the century.

A. where        B. when C. why           D. that