The boy (writes/to write)the letter needs a pen.为什么用to write

The boy (writes/to write)the letter needs a pen.为什么用to write The boy to write this letter needs a pen.的词法与句法 老师,请问英语中在什么情况下使用不定式?比如"The boy to write this letter needs a He wants to write a letter.He writes it to his pen pal.缩写成He He needs a pen to write ( ) I use the pen ________a letter?填什么?to write write a letter to the sunday mail write a letter to the chairman Write a letter to pen friend saying write a letter to your pen friend in the USA to tell them th ____(用）the pen to write letter.根据中文填空； TO write the acticle,she needs () A some more informationsC