用 over, between, along, in front of, behind, 或 across 等介词或介词短语填空 1. A lot of birds are flying ___ ____ the river. 2. The teacher is standing _____ _______ the blackboard. 3. I am running __ _____ the Great Wall( 长城 ). 4. They are swimming __ ____ the river. 5. I am sitting ____ _____my brother and my sister.