couldn’t ______. The line was busy. [ ]

It is difficult for children to change their eating habit later in life _____，parents should encourage healthy eating from an early age

My mother ___ here last Saturday. She ____in Nanjing. She ____back now.

Must I stay here with you—No, you_____. You may go home, but you ______ go to the net bar.

.None of them ______ myfriends.