Andrei has a glass tank that he would like to fill with marbles and water.
a) He starts by placing marbles in the tank and then fills the empty spaces with water.
b) He fills the tank with water first and then adds marbles on top.
c) Andrei decides to alternate layers of marbles and water until the tank is full.
d) Initially, he places marbles at the bottom, followed by a layer of water, and repeats.