请教白勇上的一题

10． The fear of rabies is well founded; few people are known to recover from the disease 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）there are few known people who have recovered from the disease once the clinical symptoms have appeared
（D）after the clinical symptoms appear，there are few known people who have recovered from the disease
（E）recovery from the disease is known for only a few people after the clinical symptoms appear

答案是b，我选a，注解上说：（分号）前后需使用完整的句子形式，但不知道a哪里不对，不也是完整的句子吗？