I think so不能表示认同！因为维基词典对“I think so”这样解释：I believe that is the case, but am not certain.
相当于我们常说的：“maybe”，maybe是一种毫无把握，不清楚的含糊回答。所以你如果说I think so，外国朋友会心想：Is that a yes or no? 到底是认同还是不认同？
例如：
Boss：Did you do your work?
你工作做完了吗？
You：I think so.
我想是吧。
(PS：这样回答，老板会疯的，你到底做没做完！)
表示认同，可以这样说
I thought the same thing.
嗯，我同意
That's what I was thinking too.
我也是这么想的
That makes two of us.
我们想的一样
接下来给大家介绍如何灵活多变地表达自己的观点，不用再一味的说 I think
01、As far as I am concerned
对我而言，从我的角度来说
例句：
As far as I am concerned, life is short, and we must achieve something during our life.
就我而言，生命是短暂的，我们必须在我们的有生之时实现某样东西。
As far as I am concerned, the matter is closed.
对我来说，事情已了结。
02、From my point of view/perspective
依我看，以我的观点看
例句：
From my point of view, social development brings lots of pollution.
依我看，社会的发展带来了很多污染。
From my perspective, those are his weaknesses.
作为我个人的观点，这些就是他的弱点。
03、From where I stand
从我的立场看
例句：
From where I stand, what he said is reasonable.
依我看，他说的话是有道理的。
From where I stand, it's a quite controversial problem.
从我的立场看，这是个颇有争议的问题。
04、It seems to me that...
我觉得……
例句：
After mature reflection it seems to me that this could not have been effected through natural selection.
经过审慎考虑之后，我认为这种结果似乎不是通过自然选择得来的。
It seems to me amount to the same thing.
在我看来，根本就是一回事。
05、I take the view that...
我所持的看法是……
例句：
I take the view that sometimes in life we have to take chances in order to make progress.
我认为我们一生中有时候必须冒险以求得进步。
06、I am of the opinion that...
我的意见是……
例句：
I am of the opinion that this new trend has both advantages and disadvantages.
我认为这种新的趋势既有利也有弊。
07、I hold the view that...
我认为……
例句：
I hold the view that a wealthy person is one who is knowledgeable and wise.
我认为博学而有智慧的人才是富有的人。
08、I argue that...
我认为……
例句：
I argue that people are born equal.
我认为人人生而平等。
09、As for me, I...
至于我，我……
例句：
As for me, I will stick to the undertaking.
就我而言，我要把这项事业坚持下去。
10、Personally speaking
就我个人而言
例句：
Personally speaking, searching and enriching the experience of life is the real meaning of travel.
对我来说，旅行的意义是寻找和丰富生命的体验。
此外，在表达某个观点或者立场时，也可以直接去掉「我认为」这一意思而直接描述现象和观点，这时表达方式就会灵活很多。
01、It is an inescapable fact that...
（什么）是一个无法回避的事实
例句：
It is an inescapable fact that some students behave badly and damage the learning environment.
有一些学生行为恶劣并且破坏学习气氛的问题是一个无法回避的事实。
02、... be noticeable
（某种现象）十分显著
例句：
The differences between the British and American academic systems are noticeable.
英国和美国的学术体制差别十分显著。
03、The underlying cause of sth. is...
某现象的深层原因是……
例句：
We should look into the underlying cause of this problem.
我们应该从更深一层去剖析这个问题的原因。
04、One possible solution is to...
一个也许可行的解决方案是……
例句：
One possible solution is to provide more sports facilities to encourage a more active lifestyle.
一个也许可行的解决方案是提供更多的运动设施以鼓励更积极运动的生活方式。
最后：
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