Microscopic plants called algae grow inside the top layer of sea ice in the Antarctic if enough sunlight reaches that layer of ice and enough seawater, which contains nutrients, reaches that layer after splashing onto the surface. Even though moderate snow cover reduces the sunlight that filters into the top layer, sea ice with moderate snow cover typically contains even more algae in the top layer than does sea ice with less snow cover. Which of the following, if true, most helps to explain the apparent discrepancy? ['The nutrients on which algae rely are common in seawater throughout the Antarctic.', 'Seawater in the Antarctic often contains higher concentrations of nutrients than does seawater in more temperate regions.', 'More sunlight filters through a layer of ice than through an equally thick layer of snow.', 'As the weight of accumulated snow forces ice lower in the water, more seawater splashes onto the surface and seeps through the snow.']