[Grammar] Present perfect continuous with time expressions & without time expressions.

[Duan]

I would like to know the difference between Present perfect continuous with time expressions & without time expressions.

Present perfect continuous with time expressions:
A] We have been negotiating the contract for last 3 days.
B] We have been facing lot of difficulties in this project since 2 months.
C] She has been writing a letter since morning.
D] He has been calling you since morning.
E] The home interest rates have been increasing recently.

Present perfect continuous without time expressions: (Can these sentences be used as stand-alone? If yes, what do they imply & how do they differ from above?)
A] We have been negotiating the contract.
B] We have been facing lot of difficulties in this project.
C] She has been writing a letter.
D] He has been calling you.
E] The home interest rates have been increasing.

 

[probus]

The only difference is the one you noted in your question: in the first group the time is somewhat specified, while in the second it is not. Otherwise all are correct, with one minor proviso: the time specification usages in your first group are those commonly used in India. They would be a little different in other parts of the English-speaking world. For example,

for the last three days
for the last two months instead of since two months