You are twenty-one, a grown-up young lady old enough to make up your own mind.
你已经21岁了,已经到了可以自己做主的年龄了。
Make the best of a bad business (or job or bargain).
身处山穷水尽,力争柳暗花明。
Those planning a trip to remote areas, or intending to live in countries where drinking water is not readily available, should know about the various possible methods for making water safe.