Which amendment is not described correctly?
a. the nineteenth amendment gave women the right to vote.
b. the twenty-sixth amendment lowered the voting age to 18
c. the fifteenths amendment gave former slaves the right to vote.
d. all amendments are described correctly

The Answer is D. All amendments are Described correctly

I double checked it.

NB:  the fifteenths amendment only fully realized about a century later. It's very hard to accept especially at Southern united States

The correct answer to your question in reality is D - that all of the amendments are described correctly. Having said that, all of them which you've provided here were correct. I've also rechecked if there was something else to add to these answers but in reality there wasn't.