Answer: See explanation
Step-by-step explanation:
It should be noted that while for is used with a period of time, on the other hand, since is used when one wants to refer to a specific point in time.
a. I have been swimming in the river (for) two hours.
b. They have been chanting Ramayana (since) 7 O’clock.
c. Aarya has been writing a letter (for) thirty minutes.
d. John has been living in refugee camp (since) 2018.
e. It has been raining (for) a long time.
f. PM has been taking meeting on the issue of J&K (for) three hours.
g. All the members of institute have been taking virtual meeting (since) 9 O’clock