Answer:
C. For each bolt the number of cracks decreased by an average of 1/2.
Step-by-step explanation:
Consider the points (2, 8) and (8, 5) on the line.
The number of cracks decreased from 8 to 5 while the number of bolts increased from 2 to 8. Thats a ratio of -3 : 6, which supports choice C.
