51.

1. useful
2. unbeneficial
3. strong
4. mixed

52.

1. steps
2. pace
3. responses
4. breath

53.

1. Suffering from
2. Confronted with
3. In relation to
4. In the face of

54.

1. avoid
2. hinder
3. delay
4. fuel

55.

1. at hand
2. in hand
3. to hand
4. by hand

56.

1. in
2. to
3. at
4. on

57.

1. tend to
2. attendant upon
3. prone to
4. subjected to

58.

1. sensory
2. sensible
3. sensational
4. sensitive

59.

1. affect
2. hinder
3. avoid
4. shape

60.

1. temporary
2. permanent
3. unconquered
4. formidable

(Reference keys.)