How does the gerund function in the sentence?

- Our field, engineering, has made great advances in fire safety.

A) Direct object

B) An appositive

C) Subject

D) Indirect object

In this sentence it should be B. An appositive.

It can easily be recognized by the commas that separate it from the rest of the sentence and it is used to describe further the subject that is "our field".

The correct answer is B : An Appositive, you can tell by the commas that parts it's from the rest of the sentence.