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消防队员们终于扑灭了加利福尼亚的一场森林大火。(时态发生在过去，强调对现在的影响）
At last firemen have put out a big forest fire in California.
forest虽然是名词，但在句中起形容词的作用，修饰fire。
since then
从那时起，到现在为止
find out
表示经过研究、努力等“找出”、“查出”：
I'll try and find out the name of the person who saved my life yesterday.我将设法查出昨天救我命的那个人的姓名。（这里find out的宾语是个从句）从句，火怎样开始的
从那时起，他们一直试图找出起火的原因。
2、Since then, they have been trying to find out how the fire began.
森林火灾时常由破碎的玻璃或人们随手扔掉的香烟头引起
3、Forest fires are often caused by broken glass or by cigarette ends which people carelessly throw away.
昨天，消防队员仔细查看了地面，
4、Yesterday the firemen examined the ground carefully ，
但未能发现碎玻璃。
5、but were not able to find any borken glass .
