The graph shows how many cups of food are in an automatic pet feeder after given numbers of days. which statement is correct?

a.
every3/4-day, the amount of food decreases by 1 cup.

b.
every day, the amount of food decreases by 4/3 cups.

c.
every 3 days, the amount of food decreases by 4 cups.

d.
every 4 days, the amount of food decreases by 3 cups.