Plasma Membrane Proteins and Cytoskeletal Attachment
a. Membrane proteins are responsible for both cell to cell recognition and cell anchoring and are stabilised by linking through to the microtubulele cytoskeletal ﬁbres.


Not entirely correct as you yourself pointed out that integrins attach to actin filaments.


  b. A protein that is enzymatically active and membrane-bound will function significantly differently to a protein that is enzymatically active and cytosolic.


Possible but not necessary.


  c. Membrane proteins are manufactured in the internal cavity (lumen) of the rough ER.


They are secreted in the ER and modified there too but not manufactured there.


  d. Damage to the smooth ER could alter the makeup of the molecules that are displayed at the cell surface.


Seems correct because the statement itself does not claim certainty. It says that the makeup of cell surface molecules (which could be lipids or proteins) could change in response to SER damage.