1. Could I borrow a pen and three pieces of paper?
能借我一支笔和3张纸吗?
还能这样说：
Can you give me a pen and three pieces of paper?
Would you lend me a pen and three pieces of paper?
应用解析：
a piece of cake 轻松愉快的事情;
break into pieces 使成为碎片;
by the piece 按件计算
come to piece 破碎，碎裂;身体(精神)垮下来;崩溃
2. I want to write a letter to my pen friend.
我想给我的笔友写封信。
还能这样说：
I want to write to my pen friend.
I would like to write a letter to my pen friend.
谚语：
Never write what you dare not sign.
不要写你不敢署名的文章。
3. My dear mother. I am missing you very much.
亲爱的妈妈，我非常想念你。
还能这样说：
Dear mom, I miss you so much.
To my great mom, I miss you terribly.
谚语：
Poverty is the mother of all arts.
穷后而工乃是艺术之道。
4. She writes to her friend once a week.
她一星期给她的朋友写一封信。
还能这样说：
Every week, she writes to her friend.
She writes a letter to her friend once a week.
应用解析：
all at once 突然;同时;
at once 立刻，马上;同时;
every once in a while 偶尔;
once too often 又一次