A: correct. Although the "survivors" from both groups perform equally well, maybe the the VE help patients to SURVIVE!! maybe patients in the VE group are MORE LIKELY TO SURVIVE!!!! That helps to explain why doctors recommend taking VE before heart surgery.
"survivor" is quite subtle a hint! Good question!
B: "some" is too weak, and this answer choice only mentions patients not been given VE, what about patients given VE? anyone suffers from postoperative complications? not very helpful for the paradox.
C: "sometimes" is too weak. the heart performance between the two groups of patients within 6 hours are never compared. irrelevant
D: "certain categories" is too weak. Still no help to see why doctors insist on giving VE.
E: "many" is too weak. and giving placebo is never mentioned in the stimulus, irrelevant.