Amodifier results when the word or phrase the modifier describes is missing from its sentence.

The correct answer is: A dangling modifier.

Modifiers help us add more detail about our thoughts and sentences. "She spoke quickly when she saw her mother". Here, the word quickly is a modifier, modifying the word spoke. It goves more information about how someone spoke (an adverb modifying a verb).

A dangling modifier is usually placed at the beginning of a sentence, although we can also put it at the end of a sentence.

Walking on the road, a plane flew over the sky. In this sentence, we don't know who was walking on the road, so the modifier walking on the road doesn't have anything to modify.