Why is my answer incorrect?

Good day,
I just wanna ask you why one of my answer in the test always wrong when I answer it correctly. I tried to correct it again and again and yet I got an incorrect one???..why so?

You want to askā€¦

You will have to be more specific for us to be able to answer that. What is the question and what answer are you giving?
A direct link to the test would also be helpful.