Identify the Control Step in the Scenario Described

Multiple Choice

Identify the control step in the scenario described.

A) Inoculating the test microbe into nutrient medium containing lead.
B) Isolating the microbe from a contaminated water source.
C) Inoculating the test microbe into nutrient medium lacking lead.
D) Inoculating the test microbe into medium containing lower levels of lead than used initially.
E) Inoculating the test microbe into contaminated water containing high levels of lead.