Which of the Following Can Cause a Large Increase in the Activity

Which of the following can cause a large increase in the activity of the citric acid cycle?

A) activation of isocitrate dehydrogenase by ADP
B) activation of $\alpha$ -ketoglutarate dehydrogenase by Ca²⁺
C) increasing concentrations of oxaloacetate by pyruvate carboxylase
D) increasing concentrations of $\alpha$ -ketoglutarate by transamination
E) all of the above