--- Who knocked at the door?--- I’ve no idea. I just pretended nobody was at home, so I didn’t ask who ______ was.
_________ my grandfather grew older, he lost interest in everything except fishing.
It was along the Mississippi River _________ Mark Twain spent much of his childhood.
It is a fact that _________ differences between countries may cause misunderstandings in communication.
North Europe __________ Norway, Sweden, Denmark, Finland and Iceland.
I was greatly impressed __________ the speech by the mayor of Shanghai before the final voting for EXPO 2010.