Why Is CAP Said to Be Responsible for Positive Regulation

Why is CAP said to be responsible for positive regulation of the lac operon?

A) Because CAP binds cAMP
B) Because CAP binds to the CAP-binding site
C) Because CAP prevents binding of the repressor to the operator
D) Because CAP bound to the CAP-binding site increases the frequency of transcription initiation
E) Because CAP binds to the lac operator when glucose is scarce