✔ 最佳答案
The present perfect continuous tense is formed by the Present Perfect of the verb to be and the present participle.(=has been washing). It is used to express the duration of an action up to the present.suggesting the action of washing is still continuing at the moment of speaking and writing.. May continue into the future,eg:-
Tom has been washing dishes for two hours (and are still washing them)
He has been washing for two hours (05:16--07:16)
He has been washing dishes since (05:16);your posting time, and are still washing now and will probably go on washing for some time.
This tense, and the other Perfect Continuous tenses, are associated with the words "for" and "since"(see time from 05:16--07:16)
The past continuous tense:-
Formed by using was(were) and the present participle repairing.It is used to express an action that was going on during a certain time in the past when something else more important,dramatic happened:-eg:-As I was repairing my cars for two hours yesterday, I wrote the sentence.
The simple past tense:-
It is used to express an action wholly completed at some point, or during some period, in the past, eg:-I repaired my cars yesterday.