The diagram shows an investigation of blood flow in the veins of the lower arm. A cloth is tightly wrapped round the arm at point Z and the veins stand out clearly. One finger presses firmly on the vein at W. When another finger strokes the vein, as shown in the diagram, the vein lies flat between points W and Y. Four reasons are given to explain why the vein lies flat. 1 The bandage at Z prevents backflow of blood. 2 The finger pressed at W prevents more blood entering the vein. 3 A valve at Y prevents backflow of blood. 4 A valve at Z prevents more blood from entering the vein. Which are correct?

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