In Drosophila, Genes Encoding Heat Shock Proteins Are Normally Not

In Drosophila, genes encoding heat shock proteins are normally not expressed by are arrested at early transcription phase. However, if these organisms are exposed to sudden bursts of heat, transcription elongation is stimulated and the heat shock proteins are expressed. Which of the following is a possible mechanism that could account for this heat shock effect?

A) Heat causes repression of HAT expression.
B) Heat stimulates PTEFb expression.
C) Heat leads to dephosphorylation of the C terminal domain of RNA polymerase.
D) Heat causes expression of an inhibitor of PTEFb.