B. The fertilizers used by farmers contaminate the river.
The Kansas River stop was most likely the most dangerous stop of the Oregon Trail.
Rivers crossing was usually dangerous for settlers with unpredictable tides ran the risk of drowning, losing livestock, losing important supplies, or overturning wagons.
C your welcome :).
Hope it helps
Since with have both the distance and the velocity of both cars, we can calculate their velocities, which is distance/time.
Roger:
2 miles in 7.5 minutes -> 
2 miles in 0,125h -> 
Natalie
2 miles in 6.5 minutes -> 
2 miles in 0,1083h -> 
With their velocities in hand you can draw your own conclusions ;)