a. They .HAVE BEEN LEARNING......... (learn) for hours as they will have an exam.
b. She ..HAS NEVER FLIED......... (never\fly) by a plane.
c. We ...HAVE BEEN COOKING........ (cook) for three hours.
d. She ....HASN'T DONE...... (not/do) her homework but she ....HAS BEEN PRACTISING...... (practise) the piano since six o'clock.
e. We ..HAVE BEEN WAITING........ (wait) for the bus since three o'clock, but it ..HASN'T COME........ (come) yet.
f. Father ..HAS PAINTED...... (paint) the fence for half an hour.