开头：

when it comes to ..., some think ...

there is a public debate today that ...

a is a commen way of ..., but is it a wise one?

recentaly the problem has been brought into focus.

提出观点：

now there is a growing awareness that...

it is time we explore the truth of ...

nowhere in history has the issue been more visible.

进一步提出观点：

... but that is only part of the history.

another equally important aspect is ...

a is but one of the many effects. another is ...

besides, other reasons are...

提出假想例子的方式：

suppose that...

just imagine what would be like if...

it is reasonable to expect...

it is not surprising that...

举普通例子：

for example(instance),...

... such as a,b,c and so on (so forth)

a good case in point is...

a particular example for this is...

引用：

one of the greatest early writers said ...

"knowledge is power", such is the remard of ...

"......". that is how sb comment ( criticize/ praise...).