Final answer:
Infinitives in English are commonly preceded by the preposition 'to.' Therefore, the answer is B) Preposition.
Step-by-step explanation:
In English, infinitives typically have a 'to' in front of them, which is part of the infinitive form of the verb.
For example, in the sentence 'I want to eat,' 'to eat' is the infinitive form of the verb 'eat.'
Therefore, the answer to the question 'In English what do infinitives normally have in front of them?' is a preposition, which in the case of infinitives is always 'to.' So the correct choice is B) Preposition.