Final answer:
The best explanation for the success of massage therapy in promoting weight gain and social interaction, and decreasing distress in low-birth-weight infants is that touch is the best developed sense at birth and is the most effective avenue for soothing and regulating newborns.
Step-by-step explanation:
The best explanation for the success of massage therapy in promoting weight gain and social interaction, and decreasing distress in low-birth-weight infants is that touch is the best developed sense at birth and is the most effective avenue for soothing and regulating newborns. Newborns have a well-developed sense of touch and respond positively to soft stroking, cuddling, massages, and warm baths. These interactions help infants feel comforted and secure, leading to better weight gain and social interactions.