The correct answer is: to.
The preposition “to” is used to indicate the person or thing that is the recipient of an action. In this case, the action is “attending” and the recipient is “the complaints of the customers.”
The other options are incorrect because they do not make sense in the context of the sentence. The preposition “at” is used to indicate a location, but there is no location mentioned in the sentence. The preposition “over” is used to indicate a period of time, but there is no period of time mentioned in the sentence. The preposition “with” is used to indicate a relationship, but there is no relationship mentioned in the sentence.
Here are some examples of how the preposition “to” can be used in other sentences:
- I went to the store.
- I gave the book to my friend.
- I am looking forward to seeing you.
- I am committed to helping others.