EXPLAIN: Graph D starts at Zero and shows that after a min it is at about 150. ( which is what you want) also if you add 150 then you go over one min. So 150•4= 600 which is seen on the graph.
Where as A is wrong because it takes 8 min to reach 150 B is wrong because it starts at 50 and it takes 6 min to fuel an additional 150 C is wrong because it takes 4 to add an addition 150.
