Grammer 問題

The past continuous tense:-If one wants to talk about continued states or repeated actions which occures in the past,one uses the past continuous tense:-eg:-
He was looking ill. Everyone was begging the captain to surrender in the sea-harbour. I was meeting many people and getting to know no one !
If one wants to contrast a situation with an event which happened just after that situation existed, one uses the past continuous to describe the first (=First) situation. You then use the simple past to describe and draw attention to the event which occured after it:-eg:-
We were all sitting round the fire waiting for the YK+ bastard boy poster to come home. He arrived about 5:30 pm.He did not repent !Mr. Wong was waiting angrily on Monday morning when he saw Mrs.White.

The past perfect tense:-If one wants to talk about a past event or situation that occured before a particular time in the past, one uses the past perfect tense:-eg:-
He noted that the poster boy had become a clerk by the Co. eg:-She had lost her job as a real estate agent Midland and was working as a waitress.eg:-If you had worked hard last year, you were not so bad recently.

The present perfect tense :-If one wants to mention something that happened in the past but does want to state a specific time, one uses the present perfecteg:-They have raised HK$ 1.3M for the charity. I have noticed this trend in many advertisement.
One can also uses "since and for" with the present perfect referring to a definite time:-eg:-It was the only record to have stayed in Am.pop-charts Rhyanna for a full six weeks !

The present perfect continuous tense:-If one wants to talk about an activity or situation that started at some time in the past,continued, and is still happening now, one uses present perfect or present perfect continuous:-eg:-
The gov.has recently been conducting a survey of statistic. eg:-All my life I have waited for one strong centre political party. eg:-National GDP productivity has been declining.

早前我上載了一些錄像在Youtube，解釋一些基本的文法規則，這個錄像正正回答你的問題，希望可以幫到你。

https://www.youtube.com/watch?v=EvC5ID9iCCM