It took them a whole period to do the listening exercise.(前面三个空的话,后面要两个空)
They spent a whole period on the listening exercise.
They spent a whole period doing the listening exercise.
It took them a whole period to do the listening exercise.(前面三个空的话,后面要两个空)
They spent a whole period on the listening exercise.
They spent a whole period doing the listening exercise.