He is not easy-going, but his trust in his friends will last forever once _______.

Shackleton kept his promise ____he would return to Elephant Island ____the crew had been left.

—Was his father very strict with him when he was at school？—Yes, he had never praised him _______ he became one of the top students in his grade. 

_______in the ocean, it becomes powerless once it is on the beach. 

There are nearly one hundred foreign students in our university, most of _______ are from America and Australia.