present perfect 1

[bayan said]

Hello!In this messageI`ll ask one big & irritating question ..In this question I`m dealing with a very important & difficult matter:present perfect,
in fact I`ve understood the whole grammar of this tense but have one idea that hasn`t been clearified by any teacher or even expert I`ve met&I hope you`ll answer fully & make me understand it but befor that please make all your talk & explanations about British English only no thing to do with AE.( I`ve read"the exact time at which an action happened isn`t important"what did the writer mean by"it isn`t important"& when is it important?, on the other
hand I`ve read"sometimes the speaker mayn`t mention a specific time but they do have one specific time in mind"how do we know that the speaker has that specific time in mind if the time isn`t mentioned?this is point1.point2 is that I`ve had several examples which I don`t know why the past simple/present perfect is used.-A-"I`m very angry because he shot my dog"
why didn`t the speaker say "because he`s shot my dog",as there`s a present result?-B-compare1-"I`ve accepted an invitation to Terry`s house for dinner"but"I received an invitation to Jannet`s party,I can`t wait to go!" why is the present perfect used in the first one but not in the second one?
-C-why is it possible to use both the past simple & present perfect in this sentence"I`m afraid I tore/have torn the news paper so it`s difficult to read"
D-"Have you ever seen a magic show?~no,but my sister saw David copperfield"why is the past simple used with"saw"& not the present perfect although the time isn`t mentioned"-E-"I`ve drawn several pictures today,I drew them on drawing-paper"when I asked an english teacher why we used the past simple in the second one but the present perfect in the first one,he said"because when talking about a verb that has been already talked about we use the past simple & because "on drawing-paper"so what did he mean by"because of 'on drawing-paper'"?-F-"we`re engaged to be married,you`re the first people we`ve told -except for my parents-Why is the present perfect used with "told"-G-I`ve read"we`re happy because you`ll marry our daughter.We give our consent to your engagement.Though we`ve only met you once when you came here for a short time last christmase "why is the present perfect used with"meet"although there`s a specific time (i.e when you came here for a short time)-H-"In different parts of England,there`re different pronunciations"~"yes!I noticed that"why didn`t the speaker say "I`ve noticed that",since he didn`t mention when & because I`ve met some phrases like"I`ve noticed etc.."?( there`re other examples in the next message)thank you very very much for answering in advance.

[Tdol]

I'm trying to catch up with a backlog of post, so will return tomorrow when I've cleared some, but would say this:
A-"I`m very angry because he shot my dog"
The person could be angry years after the dog was shot, which could explain the use of the past, but if the shooting were more recent, then the present perfect would be the form for me.