51.

1. payoff
2. pay up
3. pay for
4. pay out

52.

1. principle
2. criterion
3. custom
4. deal

53.

1. to be
2. having been
3. being
4. is

54.

1. profit
2. advantage
3. benefit
4. commission

55.

1. sending
2. transmitting
3. delivering
4. dispatching

56.

1. convincing
2. valuable
3. unusual
4. priceless

57.

1. came
2. pulled
3. headed
4. pushed

58.

1. problem
2. question
3. talk
4. saying

59.

1. Interestingly
2. Unfortunately
3. Particularly
4. Amazingly

60.

1. kissed goodbye to
2. got rid of
3. lived up to
4. made up for

(Reference keys.)