15．听下面一段材料，回答19～21题． 19．What do we know about Mary？ A．She can't decide where to go． B．She has too many pictures to show． C．She can't think of a topic forher composition． 20．What does Jack suggest Mary do？ A．Take a trip． B．Ride a horse C．Write about her trip 21．Why does Jack have to leave？ A．He's got to write his owncomposition． B．He's goingto pack for the trip． C．He's going to pick up somephotographs．
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