1. Talking about something STARTING in the past but CONTINUING up to the present：

　　-How long have you been working for the company？

　　-I've been here since I left school.

　　-Have you finished that filing？

　　-Yes， I've just put the last letter away.

　　2. Writing or saying something has happened which is STILL RELEVANT for the present：

　　We have received notification of your visit…

　　We have booked a room at the Plaza Hotel for the 16th March 19——

　　3. Refering to finished events that have a NEWS VALUE：

　　We've signed the contract with OBM.

　　Vandebrinck have at last patented their new automatic packing technique.

　　I've invited Jacques Lacroix over for lunch to talk about the new site plans in Le Havre.

　　4. Referring to events which took place IN THE PAST：

　　We despatched the shipment， as requested.

　　They interviewed Roland Thoreau for the job， but he didn't get it.

　　Because we did a lot of advertising， we sold a lot of products last year.

　　5. Sometimes the ways of referring to the past can be used together：

　　- Have you been to the trade fair yet？

　　- Yes， I have. I went yesterday.

　　- And did you see anything worth buying？

　　6. The past and the present can be closely related：

　　- And you still working on that report？

　　- Yes， I am. I've been drafting a new introduction.

　　- Mr. Casagrande has travelled all over the world， but now he's working for our office in Kuala Lumpur.