---Lucy, is maths difficult to learn in a foreign school? ---I’m not sure, but no subject can be learned well __________hard work.

---Why does the boy bring a chair here?---Because the bookshelf(书架) is half a metre __________ his head. He has to stand on it to get the books on it.

The accident happened ________ the afternoon of April 15.

The river goes _________ the city and many people like to have a race to swim ________ it every summer.

Sydney Opera House ______ a usual theatre and it symbolizes Australia.