1·She was his pen friend.
她是他的笔友。
2·I have a pen friend.
我有个笔友。
3·Everyone in Caitlin's class was supposed to choose a pen friend from another country.
凯特琳班上的每个人都应该选择一个来自其他国家的笔友。
4·I met her as a pen friend in my home country of South Africa.
我的家在南非，最初我和红通过交笔友而互相结识。
5·Everyone should have a pen friend.
每个人都应该交一个笔友。