同意楼上所说。我也学到了一招。当时一看我在想这个是转折，从一种意思转到

另一种意思。LS说对比是恰当的。

附上whereas的解释。
<--- Collins Cobuild English Dictionary --->
whereas
where.as
   whereas
  You use whereas to introduce a comment which contrasts with what is said

in the main clause.
Pensions are linked to inflation, whereas they should be linked to the cost

of living...
  CONJ
  = while

<--- 美国传统词典[双解] --->
whereas
where.as
AHD:[hwar-ǎz′, war-]
D.J.[hwe?rˋ?z, we?r-]
K.K.[hw?rˋ?z, w?r-]
conj.（连接词）
It being the fact that; inasmuch as.
有鉴于：出于…事实，鉴于
While at the same time.
同时
While on the contrary.
然而；但是；相反
n.（名词）
An introductory statement to a formal document; a preamble.
“鉴于…”：正式文件的介绍性陈述；开场白
A conditional statement.
条件性陈述