常见的连接词有though, although，as, while, even though
区分though，although，as
eg：Although/though he is a child, he can live by himself.
as 表示虽然的时候，要进行倒装;
Child as/though he is , he can live by himself.
eg：Although/though she works very hard ,she makes very little progress.
Hard as she works, she makes very little progress.
Although/though she is young, she has travelled to many countries to put shows .
Young as she is, she has travelled to many countries to put shows .
while：连接两个句子，表示虽然，但是;
eg：He is experienced while he is young.
真题分析：
1.The anti-virus agent was not known
(直到一名医生偶然发现了它)
until a doctor find it by chance.
2.I would prefer shopping online to shopping in a department store because __________(它更加方便和省时)
it is more convenient and timesaving.
3.But since water is much cheaper than wine, and many of the fancier brands aren’t available in stores, most diners don’t notice or care.
4. While there’s no question that continuous stress is harmful, several studies suggest that challenging situations in which you’re able to rise to the occasion can be good for you.
