【正确答案】[参考范文]
Dear Professor Johnson，
It's been a pleasure to write to you．We are planning to hold a lecture next Saturday evening. We know that you are a famous psychologist and you have done a lot of research on student psychology. So we are inviting you to give us a lecture on psychological preparation before tests, so that we can learn more about ourselves and do better in tests. The lecture will be held in Room 505 at 6:30p.m. next Saturday. About 80 students will be attending the lecture.
Your efforts will be highly appreciated. We are looking forward to your early reply.
Yours,
Li Ming