Your school is going to hold a speech contest,write a letter

Your school is going to hold a speech contest,write a letter to one of your foreign teachers and invite him/ her to be the judge.
你的学校将举行一场演讲比赛,给你的一个外教写封信并邀请他来做评委.
这里的词组有：
be going to do sth.
有三层含义：
①表示打算、计划或决定要做某事.如：
We're
going to spend our holidays in Wales this year． 今年我们打算到威尔士度假.
②用以表示某事物即将发生或很可能发生.如：
I'm going to be twenty next month． 下个月我就二十岁了.
③有迹象表明即将发生的动作或状态.
write a letter to sb.：write to sb.
写信给某人
invite sb.to (do) sth.
邀请某人做某事