51.

1. remark
2. reveal
3. involve
4. mistrust

52.

1. accident
2. jam
3. rush
4. death

53.

1. inhabitants
2. drivers
3. males
4. pedestrians

54.

1. possesses
2. had
3. obtains
4. have

55.

1. firm
2. poor
3. good
4. dependent

56.

1. harden
2. study
3. struggle
4. combat

57.

1. overtaken
2. explored
3. undertaken
4. regarded

58.

1. tackled
2. recognized
3. shifted
4. threatened

59.

1. such
2. just
3. so
4. also

60.

1. eliminated
2. knocked
3. sought
4. adjusted

(Reference keys.)