Researchers using a dendrograph found that the trunk diameter of a beech tree increased and decreased slightly on a daily basis and that this variation correlated negatively with transpiration rate. Under which of the following sets of conditions should the daily changes in trunk diameter be the highest?

a. cool spring day, no wind, soil partially frozen
b. hot summer day, windy, low soil moisture
c. hot summer day, windy, high soil moisture
d. cool spring day, no wind, high soil moisture
e. hot summer day no wind, low soil moisture