That paint is wet, you ___ touch it.
Each of the students, hoping to pass the exam, _____the book.
He told me the news_____, believe it or not, he had earned $1 000 in a single day.
The research is so designed that once _____ nothing can be done to change it.
If _____ carefully, the experiment will be successful.
----- When was the People’s Liberation Army’s Navy founded? -----It ____the April of 1949.