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