The research is so designed that once ____ nothing can be done to change it.  

—Have you ever been to Washington?---Yes, ____shall I forget ___ it for the first time.

They went into a small house but ＿＿＿. 

Not until he promised to return it to me as soon as possible ____ my electronic dictionary to my classmate.

I have been living in the United States for 20 years, but seldom ______ so lonely as now.