"For the last few years, I HAVE WORKED on the underground."
since : to say that something started at a POINT IN TIME in the past, and is still continuing
"Since 2006, I HAVE BEEN WORKING on the underground."
for : when you state the LENGTH of time that something has been happening
• We have known each other for ten years.
• I had been waiting for hours.
• I haven't seen him for ages.
For the last few years, I HAVE WORKED on the underground."
duration : used when something happens or changes within a TIME PERIOD with a definite start and finish.
During the concert, some child kept saying, "Is it nearly over yet?"
During her first year in college, she dated a lot a students.
"During the Uni. summer vacation last year , I WORKED on the underground."
within : tickets go on sale for a concert. There is a PERIOD OF TIME stretching from when they go on sale, till they are (i) sold out or (ii) a few minutes before the show starts. 'within' refers to a shorter period of time, from when tickets go on sale, and ending before the expected end. The shorter period of time occurs WITHIN the longer period of time.
Tickets were sold out WITHIN two hours of going on sale."
"33 per cent offended again within two years of being released from prison."
They are released from prison, and the expectation is that they will not re-offend before they die (the end of the time period). But they "re-offended within two years" of being released.
……………………………
"Because she was badly frightened, the girl remained outwardly calm."
"Although / Though she was badly frightened, the girl remained outwardly calm."
'being' is used to give the reason for something:
"Being a quiet sort of person, I didn't want to get involved."
"You can't expect them to sit still for that long, children being what they are."
"Being badly frightened, the girl remained outwardly calm." ?????????
'being badly frightened' is NOT the REASON why she remained calm:
"Despite being badly frightened, the girl remained outwardly calm."
compare
"Being badly frightened, the girl's hands began to shake."
We can't use 'being' in your given sentence.