He is faced with a lot of difficulties,|||||||| he will never give up.
A while B besides C nevertheless D however
nevertheless和however都可表示转折，这里选什么？为何？
二个分句之间为逗号，连接词要么应该是并列连词，要么是从属关联词。however和nevertheless都是只不过连接副词，没连词功能，用在逗号之后为语法错误。所以只有while作为从属连词，引导让步状语从句为唯一语法正确的句子。
