In the years after he left the White House, Richard Nixon strove to burnish his image for history more assiduously than did any former president.
(A) more assiduously than did any former president.
(B) more assiduously than any other former president.
(C) with an assiduousness unmatched by any former president.
(D) with more assiduousness than did any other former president.
(E) more assiduously in comparison to any former president.