--- Why don’t we buy a table ? --- Didn’t we just have _____．But ______ need some repair．

—Shall we go out for a walk?—Sorry. This is not the right ____ to invite me. I am too tired to walk. 

Although ______ for many years, the two old sisters recognized each other at once.

It is always difficult being in a foreign country, __________if you don’t speak the language.

The research is so designed that once________nothing can be done to change it.