What is the main idea of the Greedy Heuristic for Binary Knapsack?

a$.$ Pick the item with the highest remaining capacity at each iteration.

b$.$ Pick the item with the highest volume$-$to$-$value ratio at each iteration.

c$.$ Pick the item with the lowest value$-$to$-$volume$-$ratio at each iteration.

d$.$ Pick the item with the highest value$-$to$-$volume ratio at each iteration.