同学你好，该知识点来自沪江网校《【Uni智能】高中水平进阶托福105分【北美全能畅学班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好，解答如下，希望能帮到你：
whereas可以用在句首，助助这边整理下其用法给到同学，并对比相似词，希望能帮到你：
1. however和whereas
*You can't use 'however' and 'whereas' in the same way. Follow these general rules in order to avoid grammar mistakes:
However和whereas的用法不同。请遵守下面的规则，以避免错误。
Use 'however' (followed by a comma) at the beginning of a sentence to contrast with the previous sentence:
在句首使用however（后面要加逗号）来表示和前一句意思相反。
Some people believe that schools are responsible for the behaviour of their students. However, others argue that discipline is the responsibility of parents.
*Use 'whereas' (after a comma) to contrast two ideas in the same sentence:
*Whereas用于同一句内的两个相反意见（前面要加逗号）。
Some people believe that schools are responsible for the behaviour of their students, whereas others argue that discipline is the responsibility of parents.
*You can use 'on the other hand' or 'by contrast' in the same way as 'however'. You can use 'while' instead of 'whereas'.
On the other hand和by contrast的用法和however相同，而while和whereas的用法一样。
2. while, whilst, whereas
While and whilst are the same, but whilst is a bit more formal (according to one famous grammar book).
While和whilst一样，但whilst要更正式些（一本著名的语法书这么说的）。
*Whereas is always used for contrast. While/whilst can be used for contrast, or to mean at the same time.
*Whereas总是用于表示相反的意见。While和whilst既可以表示意思相反，也可以表示“与此同时”。
As can mean because or exactly at the moment when.
As可以表示“因为”，也可以指“就在那时”。