D. The word shadow draws attention to the narrators confusion
Step-by-step explanation:
This paragraph explains the conflict felt by people connected to troops who are fighting a war they cannot support as they do not understand what the war is actually for.
The narrator is concerned about the father but also does not understand why that war is necessary to be fought so he cannot support him completely either. This dilemma is presented as an elusive shadow which adds to the tone of the passage.