Why does it make sense for scientist to test just one variable at a time in an experiment?

Babies with very low or very high birth weight are less likely to survive. observe a graph of the data. me % babies born at different weights - babies born in that category which statement is a valid claim that could be made using the data in the graph? directional selection is occurring because the graph favors an extreme. mark this and totum save and exit next submit type here to search