Liat,
Let's not "muddy" up the water on present perfect by starting another debate on "Mr." vs. "Mr". Event the experts have varying opinions. I understand that you have probably an image that my English is not quite native, which is ok. I take no offense. Debates are based on what you know and how you see about certain things which is the case here. Is there anything wrong with "debatable"?
Now back to the present perfect questions about using "ago" and "past time", The rule of thumb the I’ve learned is this:
Present perfect tense goes with “since” and “for”, much like a an elegant carriage goes with horses. Of course, we can put a couple of “donkeys” in front of the carriage, much like using “ago” and “yesterday, or “past few weeks” with present perfect.
The carriage still moves along, but not very gracefully. Here is some write-ups about present prefect use with prepositional and time phrases. Perhaps it may be helpful for some.
http://www.geocities.com/SiliconValley/2527/presentperfect.html
Simple Past
1. The simple past is used to talk about completed actions in the past
2. The simple past is often used with expressions that refer to points of time in the past
|
at |
4 o'clock/2.12/the end of year/Christmas |
|
on |
Tuesday/19th March/the 21st/New Year's Day |
|
in |
January/1999/the 1990s/summer |
|
no prepositions |
yesterday/yesterday morning/last Monday/next April/a few days ago/ the day before yesterday/when I was young |