D) Mr. Utterson had an unusual friendship with Mr. Enfield.
The passage informs that Mr. Utterson had a “bond that united him to Mr. Richard Enfield.” This establishes that they have a relationship with each other. The passage goes on that many people couldn’t comprehend how the two men could be such friends, since they seemed to be so uninterested in each other on their walks. Despite this, they continue to highly value their weekly walk and would drop any other plans to make sure they can still go on the walk. This illustrates an unusual friendship where the two men continue to enjoy walking together even without apparent displays of social interaction.
