What activity did john snow conduct, other than mapping, that contemporary epidemiologists also use when trying to understand how to control a disease?

When creating a graph, the goes on the x axis and the goes on the y axis. a. dependent variable, independent variable b. experimental group, control group c. independent variable, dependent variable d. control group, experimental group

The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-saharan africa than among those of african descent living in the united states. even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-saharan africa but absent in the united states. discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions.

Describe two recent or ongoing space missions.