I believe the answer is C. blood vessels.
The answer would be B: It's possible that they <u>cannot produce a child with sickle-cell disease</u>, but blood tests on them both will be required to make sure.
If the sickle cell ran through the parents jeans then that'll be more of a problem, there can always be a possibility that it is in themselves, but since their parents didn't pass it down to them, their almost in the clear.
<u><em>Hope this helps!</em></u>
