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 .

Based on the preceding passage, choose your answer for question What may be the reason that Remy 's red blood cells start attacking each other ?
OPT: a. She was not feeling well .. b. The reason is entirely unknown .. c. None of the above choices .. d. She was already 13 years old ..
The answer is:
b.