Choose the most suitable option to replace the highlighted part of the sentence:
I am used to get up early every morning.

The correct option to replace the highlighted part of the sentence is to getting up.

Explanation:
In English grammar, there is an important distinction between the modal structure "used to + infinitive verb" and the adjective phrase "be used to + gerund (verb + -ing)".

1. "used to + infinitive" (e.g., "I used to get up early") is used to talk about past habits or states that are no longer true in the present.

2. "be used to + gerund" (e.g., "I am used to getting up early") means to be accustomed to or familiar with something as a habit in the present. Here, "to" acts as a preposition, which must be followed by a noun or a gerund (verb + -ing).

In the given sentence, the auxiliary verb "am" is present ("I am used to..."), indicating present familiarity or habit. Therefore, the preposition "to" must be followed by the gerund form "getting up" rather than the base verb "get up".

Thus, the correct sentence is: "I am used to getting up early every morning."