You want to invite Mr. Williams to give a
题型：问答题
问题：
You want to invite Mr. Williams to give a lecture on "American Literature" in your college. Suppose you are the assistant of the English Department, write a letter and say:
1) the purpose of the invitation;
2) the time of the lecture.
Your letter should be no less than 100 words. You don’t need to write the address. Don’t sign your own name at the end of the letter. Use Ruth instead.