11.连词+分词(短语)

有时为使分词短语与主句关系更清楚，可在分词前加连词，如when，while，if，though，unless，once等，但分词的主语和主句的主语必须为同一个。

Don't talk while having dinner．

吃饭时不要说话。

When crossing the street，do be careful．

过马路时要小心。

You shouldn't come in unless asked to．

不让你进来你就不准进来。

Once losing this chance，you can't easily find it．

一旦失去这次机会，你就很难找回。

If bitten by a snake，you should send for help and don't walk．

要是你被蛇咬了，你应当向别人求助而不要走动。

The room，although supposed to be kept locked，was often left open．

通常以为是锁着的那个房间，其实经常敞开着。