Why was the Diffie-Hellman key agreement protocol created?

A.
to eliminate the possibility of man-in-the-middle attacks, replacing the RSA method, which is susceptible to this type of attack

B.
a practical method for establishing a shared secret over an unprotected communications channel was needed

C.
an iterated HMAC function to generate pseudorandom data streams was needed

D.
to provide a scalable and secure mechanism for distributing, managing, and revoking encryption and identity information