The theme this passage best supports is found in letter "a. A person should be grateful for companionship".
Explanation:
Friday was one of the men Robinson Crusoe found during his travels around the world. The name was inspired by the day Robinson met him, and after that, Robinson taught him how to speak and behave, becoming loyal partners, then. Therefore, Friday promised to dedicate his whole life to servitude and companioship for Robinson. In this excerpt, Robinson is thankful for Friday's loyalty and partnership.
