·Sometimes the scenery on the way depends on the mood while viewing it.

分词作状语时,首先要考虑它的逻辑主语要有所指,这种逻辑主语有下列三种情况——
1、分词的逻辑主语与句子的主语一致,如：
* Enterring the dining room,he saw his mothere in a white clean overall.= When he entered the dining room,he saw his mothere in a white clean overall.—— 走进餐厅时,他看到妈妈穿着一件干净的工作服.
2、由于分词的行为者与句子的主语不一致,分词另外带有逻辑主语,如：
* The question being settled,we wound up the meeting.= When The question was settled,we wound up the meeting.问题解决以后,我们就结束了会议.
3、虽然分词的逻辑主语与句子的主语不一致,但是它的逻辑主语却是不言自明的,分词所表示的行为者,听话人或读者都知道是指“任何人/人们”,如：
* Generally speaking,this book is not very difficult.= As we/you/people generally speak this book is not very difficult.（正如人们）总的来说,这本书不是很难.
本题中的 while viewing it.就属于第三种情况,等于 while we/you/people view it.谢谢打那么多字，~·这边好像是独立主格，有逗号诶，是不是我问的那个句子也算在之内呢?主要是解释给别人听的 谢谢~·1、第一种情况是分词作状语的主要用法，第二种情况称作用作状语的分词的独立主格结构，第三种情况是分词的是一种特殊用法。2、是否用逗号是决定于分词短语在句子中的位置，放在前面一般要用逗号，如果放在后面则不需要逗号，如问题中的句子——句首：While viewing it，sometimes the scenery on the way depends on the mood. 句尾：Sometimes the scenery on the way depends on the mood while viewing it.3. 上面所举例句也可以用“连词 + 分词”表示——* He saw his mothere in a white clean overall when enterring the dining room. * We wound up the meeting after the question being settled.* This book is not very difficult if/as generally speaking.以上句子状语都在句尾，因此不需要用逗号。*