When conditions are unfavorable, some bacteria ____.

A) engage in conjugation
B) switch to photosynthesis
C) form endospores
D) become pathogenic
E) become nonpathogenic

When conditions are unfavorable, some bacteria form endospores as a way to survive in adverse environmental conditions. Endospores are tough, dormant structures that allow bacteria to withstand extreme temperatures, lack of nutrients, and other hostile conditions. This helps ensure that the bacteria will be able to survive until more favorable conditions return. Conjugation, photosynthesis, becoming pathogenic or nonpathogenic are not necessarily a response to unfavorable conditions.