Please remember to wash your hands with soap ___ the end of the experiment.
Three students in ten will go and _____ to stay in the classroom.
The beef is too expensive. I won’t buy it _____.
The medicine _____ natural plants.
----- I’m going to the States. ----- How long ______ you ______ in the States?
I don’t think _____ possible to master a foreign language without much memory work.