问一道语法题

The fear of rabies is well founded;few people are known to recover from the diesease after the appearance of the clinical symptoms.

A few people are known to recover from the disease after the appearance of the clinical symptoms

B few people are known to have recovered from the disease once the clinical symptoms have appeared.

C...

D...

E....

答案是选B，各位高手，为什么A 不对，A 也是统一时态，而且我听人说最好不要用完成时态，请指教！

这个只能说B更优