I know this sentence:
your message has been sent
the subject is no known.
I know this sentence:
you have been registered.
the subject is no known.
but what is this:
I have been really worried these past few days ?
here the subject is known , how this is good grammer? why the author not say : "I was worried" ? sorry my english is bad
The first two are examples of present perfect passive. The verbs are respectively "has been sent" and "have been registered". We do not know who did it, that is why we use the passive. Sent and registered are the past participles of the verbs send and register.
The third sentence is an example of present perfect active, where the verb is "have been" (worried is an adjective). You can put it in any tense you want, depending on the context, for example "I was worried about you but now I am fine." or "I have never been more worried in my life."
If you expand the second example further, you will see that worried can not be the verb in this sentence: "I have never been (quite) as worried about you as in these past few hours."
There's a problem over terminology here. Since ELL is about learning language, we should probably stick to the standard meaning of the word "subject" in matters of grammar. Highlighted subjects are...
Your message has been sent.
You have been registered.
The undefined but implicit referent is the agent (who/whatever sent the message, or registered you).
We assume there must be such an entity in those examples, because the meanings of the verbs involved require that there's an agent acting upon an object (technically speaking, acting on a patient).
If the agent is explicitly specified, it may well also be the grammatical "subject"...
John has sent your message.
John has registered you.
...but the agent might not be the subject even when present...
Your message has been sent by John.
You have been registered by John.
Turning to...
I have been really worried these past few days. (again, with the "grammatical subject" highlighted)
...the verb to worry doesn't normally imply an agent acting on an object/patient (there's only really you involved if you say I worry when I go to bed at night).
Semantically, there's not much to differentiate Present Tense I worry from the passive version I am worried. Essentially, the verb to worry is simply being used to create an "adjectival" worried from the past tense, but follow that link if you want the BBC's fine distinction (which I wouldn't bother too much about).
The "headline" difference between Present Perfect passive (not active, I don't think)...
1: I have been really worried these past few days.
...and Simple Past passive...
2: I was worried.
...arises from the fact that Present Perfect (as per the name) implies a stronger connection/continuity from the past to the present time (which may by extension emphasise the duration more). But this is also a "fine distinction". In practice, OP's #1 and #2 are mainly just stylistic choices.
(I can't resist putting this section in, but note that it's not relevant to all learners... :)
The verb to worry can have an agent and a patient, particularly when it has OED's sense 3a...
trans. To seize by the throat with the teeth and tear or lacerate; to kill or injure by biting and shaking. Said e.g. of dogs or wolves attacking sheep, or of hounds when they seize their quarry.
So if we can postulate a sheep who speaks English, she might say...
I was worried yesterday.
...then grammatically, she might mean either of...
That new untrained sheepdog worried me (it attacked me).
I was worried (e.g. - that the new dog might not be able to herd us back into the pen in time for tea).
