explain the gramatical roles

in the name of allah
can any one help me to explain the roles in these sentances
please
first
I _____ walking to work this way for twenty years. That's a long
time! Do you even walk in the rain
a corrected answer is have been
why is it not am or was
second
Do you like your teacher? Yes, but she always ___ annoyed when I ask questions
a corrected answer is gets
why is it not has
third
What _____ happen if all the clocks in London stopped? I don't
know. What a silly question
a corrected answer is would
why is it not will
fourth
She's got a great suntan. Yes, she _______ been somewhere sunny on her holiday
a corrected answer is must have
why is it not should have
fifth
John is always busy. He has to ______. Yes, I know. So do I
a corrected answer is work hard
why is it not work hardly
:d7:
thank to every one answer my questions