Which sentence contains a dangling modifier?

When we surfed at the beach, the waves were huge.

The waves were huge when we went surfing at the beach.

Surfing at the beach, the waves were huge.

As we surfed at the beach, the waves were huge.

The following sentence contains a dangling modifier:

C. Surfing at the beach, the waves were huge.

It is a dangling modifier sentence because of the placement of "Surfing at the beach",

The dangling modifier error occurs because the sentence fails to specify anything to which the modifier can refer.

The answer is indeed the third option: Surfing at the beach, the waves were huge.

Explanation:

A dangling modifier happens when the person or thing that should be modified isn't clear.

In the other options offered, it is very clear that the ones who were surfing at the beach were "we" and that the waves were huge.

However, in the third option, it isn't clear that "we" were the ones surfing. The way the sentence is structured, it may seem as if the waves themselves were surfing at the beach. That's why "surfing at the beach" constitutes a danging modifier.