Which of the following most logically completes the argument? A. some of the microorganisms found by the researchers are incapable of living near the Earth's surface B. some of the microorganisms found by the researchers are known to inhabit the surface soil near the researchers' drilling site C. when drilling below the Earth's surface, it is impossible to prevent contamination of the drill by surface-soil microorganisms D. it is difficult to keep microorganisms alive once they have been recovered from underneath the Earth's surface E. the drilling equipment used by the team of researchers was similar to drilling equipment used by most previous teams of researchers investigating life below the surface of the Earth