单选题 The passage implies that research into the cause of human narcolepsy has been complicated by what aspect of the human brain?

• (A) The tendency of certain neurons to resemble foreign matter that HLAs reject
• (B) A lack of apparent neurological damage caused by a tendency to remove debris through support cells
• (C) Its susceptibility to diseases like Parkinson's and Alzheimer's
• (D) Its tendency to reject the drugs which scientists have developed to treat narcolepsy's symptoms
• (E) The effects of aging on the symptoms of the disease