B. They are winds that blow in the opposite direction of a normal wind.
Answer:

Explanation:
Data provided in the question
The ratios are
Second graders to the fourth grader is 
First graders to the second grader is 
Third graders to the fourth grader is 
Now if we multiplying these above three ratios but the last ratio should be reverse
So, it would be
= 
= 
Hence, the ratio of first graders to the third graders is 
A good index fossil is one with four characteristics: it is distinctive, widespread, abundant and limited in geologic time. Because most fossil-bearing rocks formed in the ocean, the major index fossils are marine organisms. That being said, certain land organisms are useful in young rocks and specific regions.