For / Since (Crash Course)

My grandparents walk _____ twenty minutes a day.
for

How long is it _____ you visited your grandparents?
since

We have been dating _____ a long time.
for

That lady has been waiting for the bus _____ noon.
since

I studied for this test _____ three days straight
for

My family has lived here _____ last March.
since

She has worked there _____ she finished college.
since

I have been calling you _____ half-an-hour.
for

Lisa and Jill have been at the library _____ a long time.
for

My teacher has been sick _____ last Monday.
since