Many people assume the word "obsolescent" must be a fancy form of "obsolete," but something obsolescent is technically something in the process of becoming obsolete. Therefore it's an error to describe something as "becoming obsolescent."
The words 'since' and 'for' are often confused by English language speakers. There is a simple rule to follow to differentiate between the usage of these two words.
Since is used to talk about time from a specific period while For is used to talk about a length of time.
I have been living in Delhi since 11002.
I have been living in Delhi for twenty years.
I have been studying since 7am today.
I have been studying for eight hours.
My tutor has taught me since January this year.
My tutor has taught me for five months.
Heroin is a highly addictive opium derivative; the female main character in a narrative is a heroine.