1、 她三年前去了美国,至今没有回来过.( 英语翻译）
He has gone to America and he hasn’t been come till now.
2 、她去美国几年了?他去美国5年了
How many years has she been in America? He has been in America for five years.
How many years has she stayed in America? He has been in America for five years.
3、has been to Beijing / has gone to Shanghai , 这是现在完成的句型,
My friend has been to Beijing. 我的朋友去过上海（意思是现在已经回来了）
He has gone to Shanghai 我的朋友去了上海（意思是此刻不在家,也许在去上海的路上,也许已经到了上海）
【解析】
1）以下几种说法表示的意思完全不同：
Have been in … 表示一直在某地呆着,此刻还在那里.
Have been to … 表示曾经去过某地,此刻已经不在那里了,也许已经回来了.
Has gone to … 表示已经向那里出发,可能在路上,也可能已经到了.
2）five years ago 表示的是过去的时间,即“五年前的那个时候”,只能用在过去时态,如 ：
He went to Shanghai five years ago（五年前他去过上海）
3）since five years ago 表示从五年前直到说话时为止,只能与与能够在这段时间延续下来的的动词完成时态连用现在,如：
He has lived in Shanghai since five years ago（自从五年前他就在上海住了）
但是不能与瞬间动词完成时态连用,如：
He has left for Shanghai since five years ago,这样意思成了“从五年前他就离开往上海走,直到今天还没有完全离开”,这是不符合逻辑的,即使是一个瘸子也不会出现这种情况.
4）因为过去完成时表示是截止到过去的某个时间以前发生的行为,即过去的过去,因此since XX years ago也不能与这种时态连用.可以把ago改为before,就可以表示过去的过去,如：
He had lived in Shanghai since five years before. 早在过去某个时间的前五年他就在上海住过了.
4、我们会帮你实现你的梦想,你自己也要努力.
We will help you realize your dream; however, you should make great efforts for it yourself.
We will help you make your dream come true; yet you must exert yourself to realize it.