Mercedes __ (work) as a teaching assistant since she arrived here 2 years ago.
Mercedes HAS BEEN WORKING as a teaching assistant since she arrived here 2 years ago.
I __ (try) to finish my assignment all through the plane journey, but it was too turbulent.
I WAS TRYING to finish my assignment all through the plane journey, but it was too turbulent.
Working conditions in the factory __ (improve) before the new management started.
Working conditions in the factory HAD IMPROVED / HAD BEEN IMPROVING before the new management started.
I know I failed the test because I __ (not concentrate) in Professor Williams´ lectures.
I know I failed the test because I HADN´T BEEN CONCENTRATING in Professor Williams´ lectures
The whole family __ (stay) with Ralph´s parents until the building work is completed.
The whole family IS STAYING / WILL BE STAYING with Ralph´s parents until the building work is completed.
The security guard __ (lock) the office when the burglars forced their way past him.
The security guard WAS LOCKING the office when the burglars forced their way past him.
The rearranged lecture __ (take) place next Friday at 5.00 p.m.
The rearranged lecture IS TAKING PLACE / WILL BE TAKING PLACE next Friday at 5.00 p.m.
The robbery was very well organised. They must __ (plan) it for a long time.
The robbery was very well organised. They must HAVE BEEN PLANNING it for a long time.