$\begin {array} {1 1} (a)\;Stomodaeal\: Valve & \quad (b)\;Crop \\ (c)\;Ileum & \quad (d)\;Proventriculus \\ (e)\: Mesenteron & \quad (f)\: Colon \end {array}$

$\begin {array} {1 1} (1)\;D \rightarrow B \rightarrow E \rightarrow A \rightarrow C \rightarrow F & \quad (2)\;D \rightarrow B \rightarrow A \rightarrow C \rightarrow F \rightarrow E \\ (3)\;B \rightarrow D \rightarrow A \rightarrow E \rightarrow C \rightarrow F & \quad (4)\;B \rightarrow D \rightarrow A \rightarrow C \rightarrow E \rightarrow F \end {array}$