for a long time 不一定是完成时。
for a long time 可以用于一般过去时、将来时等，真正运用时对句子时态没有太大要求。
如：I won't wait for a long time. 将来时，我不会等太久的时间。
如：He always sits here after supper for a long time.
一般现在时，他总是饭后再这里坐很久。
有一些时间状语对句子时态是有限制的,比如遇到yesterday得用过去时，遇到since得用完成时态。
双语例句如下：
We sometimes argued away for a long time.
有时我们连续争论很长时间。
He is very weak, for he has been ill for a long time.
他病了很久，身体衰弱。
I puzzled over this question for a long time before it finally clicked.
我对这个问题茫然不解，过了很长时间终于明白过来。
Not for a long time, though.
但是不会保持很长时间。
For a long time I’ve thought about why people are so crazy about productivity.
在很长的一段时间里，我都在思考为什么人们总是疯狂的追求成效。
We sat there for a long time, looking at the people.
我们在那坐了很长时间，观察来来往往的人们。
Drugs have been in our schools for a long time, but never to the degree that exist now.
吸毒的情况已在我们的学校体制中存在很长时间了，但从未达到现在这样严重的地步。
This sign was one of the standard characters on all typewriters' QWERTY keyboards for a long time.
过去在相当长的时间里，这个符号是所有打字机传统键盘上标准的字符。
But for a long time Europeans have altered their landscapes, including the removal of 90% of wetlands and floodplains, which are crucial parts of river ecosystems, " he said.
但是欧洲人已改变了他们的环境有很长时间了，包括从90%的湿地和漫滩移民，那是河流生态系统的关键地带”。他说。
I run so that I can stay healthy and be in their lives for a long time.
跑步能保持身体健康，从而使我可以与孩子们一块生活很长时间。
She seemed very interested in my culture, so I talked with her about it for a long time, more like a discussion actually.
她看起来对我们的文化很感兴趣，所以我和她聊了很长时间，其实两个人更像是在讨论。
The soil contains evidence of the influence of man since the Stone Age, Böse explains, and this age has already been treated as an independent geological era for a long time.
土壤中含有着石器时代的人影响的证据，波瑟解释说，这一个时期作为一个独立的地质时代来说已经有很长一段时间了。
As a loyal football fan, I had expected the match for a long time, so after class I hurried home.
作为一个忠实的足球迷，我已盼望这场比赛很长时间了，所以放学后我就匆忙往家赶。
Some of these measures had been around for a long time, but others were new, a reaction to the attacks.
有些安全措施已经实施了很长时间，有些则是新的，作为对此次恐怖袭击的反应。
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