51.

1. to
2. for
3. of
4. in

52.

1. /
2. which
3. whom
4. who

53.

1. if
2. unless
3. even if
4. because

54.

1. like
2. likely
3. less likely
4. more likely

55.

1. rest
2. other
3. fittest
4. fitter

56.

1. active
2. lively
3. still
4. inactive

57.

1. to exercise
2. exercising
3. exercise
4. exercised

58.

1. However
2. So
3. Although
4. Furthermore

59.

1. reduce
2. reducing
3. to reduce
4. reduced

60.

1. encouraged
2. encouraging
3. to encourage
4. encourage

(Reference keys.)