He is so addicted to smoking that ________ seems to be no chance of talking him into quitting.
I failed in the final examination last term and only then __________ the importance of study.
Only when your identity has been checked __________.
The old couple have been married for 40 years and never once __________ with each other.
Only after my friend came __________.
I have been living in the United States for twenty years, but seldom __________ so lonely as now.