Are these correct sentences:

Leaping upstream, we fished most of the day for salmon.
At the age of ten, my family took a trip to Washington, D.C.
Skimming every chapter, the biology textbook made more sense.
I need help with Dangling modifiers.

Those three sentences are wrong.

Did we leap upstream?
Was the family aged ten?
Did the textbook skim every chapter?

How can you reword these sentences so that the phrases modify the word closest to them.

Study this site.

http://www.chompchomp.com/terms/danglingmodifier.htm

While we were fishing the salmon, were leaping upstream.

Is this correct

Yes, but delete the comma after salmon and place it after fishing.

Yes, the first two sentences are correct, but the third sentence contains a dangling modifier.

A dangling modifier is a phrase or clause that doesn't logically or grammatically modify the word it's intended to describe. It usually happens when the subject of the main clause is missing or unclear.

In the third sentence, "skimming every chapter" is the dangling modifier. It is not clear what is meant by "skimming every chapter." It is unclear who is skimming the chapters, which creates confusion. To fix the sentence and remove the dangling modifier, you can rephrase it like this:

"After skimming every chapter, the biology textbook made more sense."

Now it's clear that the person who skimmed every chapter is the one who found the textbook easier to understand.

To avoid dangling modifiers, always make sure the subject doing the action is clear and directly connected to the modifier.