Wow ... as they say , " When it rains it pours . " Our auxiliary backup emergency dog Remy passed away this morning . She was 13 . She was not feeling well and we took her to the vet yesterday . For some unknown reason , her red blood cells were attacking each other .

Generate a question about the above context.
What may be the reason that Remy 's red blood cells start attacking each other ?
Available options:
(I). She was already 13 years old .
(II). She was not feeling well .
(III). We do not know the reason .
(IV). None of the above choices .