I used this element in the control,
Look at my settings

I don’t know what is wrong with my approach,But the result of the operation is like this.
I used this element in the control,
I guess you added two times. Delete it and freshly add again and then check once.
What do you mean by what I added twice? Sorry, I didn’t understand.
I mean at the time of creating drop down list using Form activities you added twice that values in the list.