It’s the one with the line.
Because you have A,T or C,G or it can be in a different way like UA and CG. It closely related because it’s attached to the other letters and it comes from both parent like mom and dad. but I’m order for them to work they both have be to in the right letter for it be correct.
I hope this help. If you want I can explain it in a different way if you need to. :)