"the plasma membrane of the bacterium pseudomonas syringae is able to remain fluid when it is extremely cold. the bacterium most likely accomplishes this by"

The answer to this question would be: d. replacing saturated fatty acids with unsaturated fatty acids.

To keep the membrane liquid, the bacteria must change the fatty acid into other structure with lower melting points. Saturated fatty acid has more C-C bind, make them less kinky and be able to be packed more tightly. This structure causes them to have higher melting and boiling point. So it was more likely to be solid than liquid if compared to unsaturated fatty acid.

the intracellular content of proteins. There are anti freezing proteins that prevent freezing by disrupting the optimal alignment for water to become crystallized ice. This particular strain does have ice nucleation active proteins within the membrane to help frost to occur on plants at warmer temperatures.