a. Alice and Bob simply needs to send the photons at Sam's angle 
   and Sam's angle plus 90 degrees, so that the Sam's reflection 
   doesn't affect the channel.

b. (Unless the difference between Sam's two angles is 180 degrees...)
   Alice and Bob can't fully restore the channel,
   because even if they reset the angle to one of Sam's, 
   the other device can still change their information.

c. Alice and Bob can communicate without error, if they know at what
   angle Eve is listening and set their angle of polarization accordingly.
   (So if Eve listens at a vertical angle, then Alice and Bob should
   use vertical polarization for 1).

d. Alice and Bob can detect whether Eve is listening by sending packets
   of photons for one (classical) bit. Then, they can measure the actual 
   angle of polarization and detect any changes.

e. Since Sam can determine the angle of polarization, he can always
   adjust his reflection angle so that it's effective.

   Eve can listen without being detected by setting her tester at the
   angle of polarization.