51.(when)and (by whom)the islands of the west Indies were first settled is a matter (of debating)(among)archaeologists.

52.(Cliff's and Al's)car (broke down)again,but (luckily)they knew (how to fix)it.

53.(from the top )of the tower,Jacob was able (to clearly and easily see)the (whole )city (stretching)out below him.

54.Joan (decided)that she did not like the (girl eating)an ice-cream cone on the bus after (she)(yelled)at her little brother.

Key：

1-10BBBBD-ADCAB

11-20CCBCC-BABBD

21-30BBCCB-BACAA

31-40CCBAA-DCBAB

41-50BCADC-CAADD

51-54CABC