3．On the other hand packaging can have many disadvantages．
4．Firstly many people die of passive smoking(被动吸烟and secondly it can aggravate(使……恶化lung diseases．
相关的连接词还有：On the contrary，all in all，in short，generally，worse still，on the other hand，in conclusion，as a consequence，hence，also，personally，furthermore，definitely，surely，undoubtedly，obviously，additionally，in addition，moreover，consequently，clearly，besides，as well，likewise，in my opinion，for the sake of，last but not the least，to begin with，firstly(first，etc．
很多时候，一些常用的句式或句子也能承上启下，使相关的信息得到巧妙的过渡和衔接。例如： The main reason is that…
I can\'t agree more Another thing we can\'t forget is There is every reason to believe As we all 总而言之，一篇好的议论文，总是在结构、逻辑和语言等方面略胜一筹。
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that…
that…
know…
