51.

1. Unfortunately
2. Apparently
3. Similarly
4. Certainly

52.

1. beckoned
2. signaled
3. stimulated
4. recognized

53.

1. inflicted
2. infected
3. acquainted
4. diagnosed

54.

1. constituting
2. construing
3. constructing
4. consisting

55.

1. respectably
2. respectfully
3. respectedly
4. respectively

56.

1. snoring
2. sneezing
3. sniffing
4. yawning

57.

1. rehabilitation
2. condition
3. deterioration
4. regression

58.

1. breathe
2. to breathe
3. breathing
4. breathed

59.

1. suspected
2. detected
3. identified
4. doubted

60.

1. may be presented
2. may present
3. maybe present
4. may be present

(Reference keys.)