A grocery clerk made this graph to relate the number of pounds of peaches and plums to the cost.

Which statement is true based on the graph?
A. The quantities form a proportional relationship for both peaches and plums.
B. The quantities form a proportional relationship for plums but not for peaches.
C. The quantities form a proportional relationship for peaches but not for plums.
D. The quantities do not form a proportional relationship for either peaches or plums.