Mom had made / had been making us dinner by the time we brought the takeout food home.
Mom had made us dinner by the time we brought the takeout food home.
Tommy had studied / had been studying all day for the test by the time he had a headache.
Tommy had been studying all day for the test by the time he had a headache.
Cindy had taken / had been taking piano lessons for years without stopping.
Cindy had been taking piano lessons for years without stopping.