详细内容：一、主动形式表示被动意义
1. 动词need, want, require表示"需要时"，后接动名词或不定式的被动式表示被动意义。如：
Your room needs cleaning/to be cleaned. 你的房间需要打扫一下。
My house requires repairing/to be cleaned. 我的房子需要修理一下。
2 在"be worth doing"短语中，动作与主语之间存在动宾关系，用主动形式表示被动意义。如：
This book is well worth reading 这本书很值得一读。
3. 在"主语 +be + adj +to do"这个句型中，不定式动作与主语之间存在动宾关系，则用主动形式表示被动意义。如：
This question is hard to answer. 这个问题很难回答。
English is easy to learn. 英语很好学。
4.连系动词(如：feel,taste,sound,smell,look等)用主动形式表示被动意义。如：
This material feels very soft. 这块材料摸上去很柔软。
This apple tastes good. 这个苹果尝起来很好吃。
5. 有些表示主语内在性质或性能的不及物动词常与一些副词连用，用一般现在时的主动形式表示被动意义，其主语一般为事物。这些动词有：sell,read, write,wash,wear,last等。如：
The pen writes smoothly 这支笔写起来很流畅。
This kind of food sells well. 这种食物很畅销。
6. Won't或wouldn't表示"不愿"时，后面的动词常用主动形式表示被动意义。如：
The door won't open. 这门就是打不开。
This box wouldn't move. 这个盒子就是移不动。
二、since和for
Since 用来说明动作起始时间，for用来说明动作延续时间长度。例如：
I have lived here for more than twenty years.我住在这儿二十多年了。
I have lived here since I was born. 我从出生起就住在这儿了。
注意：并非有for 作为时间状语的句子都用现在完成时。
I worked here for more than twenty years. (我现在已不在这里工作。)
I have worked here for many years.(现在我仍在这里工作。)
注意：用句型转换的方法，很容易排除非延续动词在有for/since结构的完成时中的误用。
1)(对) Tom has studied Russian for three years. = Tom began to study Russian three years ago, and is still studying it now.
2)(错) Harry has got married for six years. = Harry began to get married six years ago, and is still getting married now.
显然，第二句不对，它应改为 Harry got married six years ago. 或 Harry has been married for six years.(联系我时，请说明是在51站台网看到的，谢谢！)