code: def forward(self, c2, c3, c4):
      fused_feature = self.fuse(c2, c3, c4)
      out = self.block(fused_feature)
      return out
  
imports: import torch
  import torch.nn
  import torch.nn.functional
  from pywick.models.segmentation.da_basenets.segbase import SegBaseModel
  from pywick.models.segmentation.da_basenets.fcn import _FCNHead
label_desc: Use image node_id 2 for calling the _DUHead obj's underlying member method code with example usage: obj.forward(c2, c3, c4) and returns: out