51.

1. hardly
2. never
3. less
4. reliably

52.

1. fails
2. succeeds
3. results
4. rises

53.

1. resulting
2. deducing
3. avoiding
4. causing

54.

1. eliminate
2. abolish
3. cut down
4. cope with

55.

1. innocent
2. positive
3. likely
4. moderate

56.

1. delivered
2. containing
3. adopted
4. regulated

57.

1. sensitive
2. tight
3. widespread
4. rough

58.

1. has
2. emerges
3. causes
4. does

59.

1. yielding
2. handling
3. increasing
4. reducing

60.

1. trouble
2. margins
3. impact
4. threat

(Reference keys.)