Read the following context and choose the best option to answer the question.
Context: 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 .
Question: What may be the reason that Remy ’s red blood cells start attacking each other ?
Options: 
A. She was already 13 years old .
B. She was not feeling well .
C. We do not know the reason .
D. None of the above choices .


C