He seems to know French very well: he is said to have spent his youth in Paris
Present perfect is used in this sentence not because it's about youth, but because it's reported speech (somebody told you that he had spent his youth in Paris), so the tense is backshifted.
If you remove is said, it is no longer reported speech, so you don't need to backshift:
You might say whichever number you write/use. The plain form of the verb works for general statements, and this question doesn't seem to depend on a particular time of use/writing.
Also, if they are asking about the correct address, they probably haven't already sent the book.
In the first example, you're describing your hypothetical in the present simple: "...when people read your work, they get a different perspective than the one intended*" (I have to assume "read" was in the present simple that would be correct). Also, "*It's your fault..." is in the present simple. So, "... they don't get ...
It have looked like I was running away is not grammatical. It is the (dummy) subject, and requires the 3rd person auxiliary has.
Either your dictionaries are wrong, or this is embedded in some larger syntactic unit that you are not telling us.
Separately, It has looked like is not idiomatic in most contexts: we don't usually use the "present perfect&...
"It have looked..." is incorrect.
"It has looked like I was running away" is a grammatically correct, but normally unnatural sentence.
You would naturally use the past tense "It looked like I was running away."
The match has been postponed for two days means that a decision has been taken to play it two days from now instead of today. We could also say it during those two days.
He has been jailed for two years means that he has been sentenced to two years in prison (punished is not appropriate here). We could also say it during those two years.
I hope this answers ...
There are two issues competing here.
One issue is the grammatical correctness of the phrase. The other is, communicating the thing you intend so as to get the correct business or financial outcome.
The grammar of the sentence is OK as it stands. Changing "had" to "has" would also be acceptable. That seems to be the specifics of your ...
The perfect from "Who has watched it?" would be normal. You are not concerned with the time when it was watched, only the the whether they now have the experience of seeing the film.
That doesn't make the past tense wrong. If you had already established that you were talking about a particular time in the past, you might choose the past tense:
A is normal.
C is ungrmmatical in my British English dialect, whch doesn't allow a simple past with since. I believe this is not true of all varieties of English.
1B is possible but not in the circumstances you describe. When you use the so-called "past perfect" you are choosing to view the event(s) from some later time in the past; so if you are ...
The two options are not always interchangeable.
Take your "Frank" example. Version (1) states:
Frank will return the book if he has finished reading it.
This phrasing suggests that the speaker doesn't know, at the present moment, whether Frank has finished the book or not, but is stating with some certainty that Frank will return the book if he ...
If he finishes implies that the speaker thinks Frank may not manage to finish the book. (1) assumes that he will, but that he may not have done so yet.
(2) is better than (2a) because it makes it clearer that the preparations have to be complete for the project to start.
"Since", in this context, means from a particular time in the past until a later time. A 'particular' time would be a fixed event that began the time period, not the period itself.
We only say someone 'has died' when referring to their current status (ie they are dead). The fixed event is when they died, or their death. So, in your first example, ...