to as preposition or infinitive

[mundasingh123]

Last week local shrimpers held a news conference to
take some credit for the resurgence of the rare
Kemp's ridley turtle, saying that their compliance with
laws requiring that turtle-excluder devices be on
shrimp nets protect adult sea turtles.
(A) requiring that turtle-excluder devices be on
shrimp nets protect
(B) requiring turtle-excluder devices on shrimp nets
is protecting
(C) that require turtle-excluder devices on shrimp
nets protect
(D) to require turtle-excluder devices on shrimp nets
are protecting
(E) to require turtle-excluder devices on shrimp nets
is protecting


Options D and E are wrong
My question how do we find out whether "to " is used as a preposition or an infinitive

[GmatKiss]

[spoiler]IMO:B[/spoiler]

[Jim@Grockit]

Last week local shrimpers held a news conference to
take some credit for the resurgence of the rare
Kemp's ridley turtle, saying that their compliance with
laws requiring that turtle-excluder devices be on
shrimp nets protect adult sea turtles.
(A) requiring that turtle-excluder devices be on
shrimp nets protect
(B) requiring turtle-excluder devices on shrimp nets
is protecting
(C) that require turtle-excluder devices on shrimp
nets protect
(D) to require turtle-excluder devices on shrimp nets
are protecting
(E) to require turtle-excluder devices on shrimp nets
is protecting


Options D and E are wrong
My question how do we find out whether "to " is used as a preposition or an infinitive

Usually the words before "to" will give you a hint about its function when it comes before a verb (since it can't be an infinitive when it doesn't come before a verb). Some verbs generate infinitives, and infinitives can also be used as noun phrases; I wish I had a better answer than "learn about when infinitives get used, in a more detailed way" but unfortunately I can't think of a simple algorithm for infinitive-detection.

[mundasingh123]

Jim , Below is a sentence in which , i think , to is used as a preposition

His plans to conquer the city dashed, Alexander decided against advancing any further .

But " to is followed by a verb,yet to is not an infinitive here