The use of "to" as infinitive and preposition

In English "to" can be used as a preposition or as a infinitive. As an infinitive, the verb that follows it is in the present tense. For example, in the sentence, "I want to buy a book." "to" acts as an infinitive.

As a preposition, "o" followed by a noun, pronoun or ing-verb. Some examples are as follows:

1 We have to resort to force (a noun) to drive the dog away.
2 I look forward to hearing from you soon.
3 They resorted to using a make-shift shed for the stage show.
4 This is the key to my room.