Created by: XipengY

1. self.new_proposals = fluid.layers.slice(self.proposals, axes=[1], starts=[2], ends=[6])
2. self.new_proposals = fluid.layers.slice(self.proposals, axes=[0, 1], starts=[0, 2], ends=[INT_MAX, 6]) 写法1，返回的lod_level=2, 写法2，返回的lod_level=1, 写法2改变了lod_level.