Final answer:
Most social workers are women, but they serve a diverse range of clients, not primarily a certain gender. The choices provided in the question do not accurately fill in the blanks based on the given context that social workers service many different groups.
Step-by-step explanation:
The question asks us to fill in the blanks about the demographics of social workers and the primary group they service. Based on the provided context about gender roles in various professions, it's evident that certain jobs have historically been associated with one gender more than the other. Social work is one such field where there is a significant representation of one gender over the other.
Given the context provided that mentions care-related occupations such as childcare, healthcare, and social work are professions where women tend to outnumber men, and considering societal roles and expectations, we can conclude that most social workers are women and they service mainly those who need care support, which doesn’t necessarily divide by gender. Therefore, none of the options A to D provided in the student's question correctly complete the sentence as per the information provided, as they suggest a binary and specific clientele which isn't accurate. Social workers serve a diverse client base regardless of gender.