Tell me if I correct, I need to mark all the couple Structural isomers in the list(you can see in the picture)so I mark in blue all what I think is an Structural isomers.

About B I am not sure.

Thanks.

I think I can read your structures well enough to say that A, C & D ARE structural isomers.
The A's are both C5H10O2: Ethyl propanoate and Pentanoic acid.
The C's are both C5H10: 2-methyl-2-butene and 2-pentene.
The D's are both C6H12: 3-hexene and cyclohexane.
The B's are both the same compound: bromoethane.

Well if you says "The B's are both the same compound: bromoethane" so is not also a couple Structural isomers?
Thank you.

No, if you hold the first molecule in one hand and the other in another hand (the models of them, that is), you'll see that rotating one around will give you the same thing you have on the other hand.

Again you gave an great answer. REALLY thanks to both of you Unknown008 and DrBob1. I really appreciate all of your help.