The Figure Shows Plant Growth Responses to Variation in Availability

The figure shows plant growth responses to variation in availability of water. If this is an example of adaptive phenotypic plasticity, how would we expect the root-to-shoot ratio to be related to fitness?

A) When water is scarce, plants with high root-to-shoot ratios have higher fitness.
B) When water is scarce, plants with low root-to-shoot ratios have higher fitness.
C) In all environments, plants with high root-to-shoot ratios have higher fitness.
D) In all environments, plants with low root-to-shoot ratios have higher fitness.