Bunuel wrote:
The more cautious commanders of the Army of the Potomac, such as George McClellan and George Meade, chose to withdraw after costly battles, but commander Ulysses Grant's strategy
was the keeping up of pressure on Lee's Confederates even after losing a battle to them, and then he occupied positions between Lee's army and Richmond to invite another open battle.
A. was the keeping up of pressure on Lee's Confederates even after losing a battle to them, and then he occupied
B. was keeping up pressure on Lee's Confederates even after losing a battle to them, and then to occupy
C. having kept up pressure on Lee's Confederates even after losing a battle to them, he then occupied
D. was to keep up pressure on Lee's Confederates even after losing a battle to them, and then to occupy
E. was that he keep up pressure on Lee's Confederates even after losing a battle to them, and then occupying
Magoosh Official Explanation
Split #1: parallelism! Grant's successful strategy had two parts, and these two parts need to be in parallel. Grant kept up pressure, and Grant occupied a position. Those two need to be in parallel.
(A) "…the keeping up of pressure … he occupied" = complex gerund (very awkward!) + full verb = a failure of parallelism. This is incorrect.
(B) "keeping up pressure …. to occupy" = gerund + infinitive = a failure of parallelism. This is incorrect.
(C) "having kept up pressure … he … occupied" = participle + full verb = a failure of parallelism. This is incorrect.
(D) "to keep up pressure …. to occupy" = two infinitives in parallel = perfect!
(E) "that he keep up pressure …. then occupying" = full verb + participle = a failure of parallelism. This is incorrect.
On the basis of this single split,
we can isolate (D) as the only possible answer.