The capacity of the current reserve is based on its requirements. in other to expand, or improve the capacity, is to raise the requirement of the reserve.
It is just like having a pocket that can receive 100, if you want to increase the capacity of the pocket, you will need to adjust the pocket size, this is raising the pocket requirement for you to receive 200 in same pocket.
From my analogy, option B is the best answer to the question.
Social structure controls the behavior of the members of a society in different ways.
The structure of a society is what groups its members according to factors such as class, age and so on.
The members of each group in a social structure are expected to behave in a certain manner, Like in the social structure, children are subordinates and therefore are supposed to be adherent to their parents.
Case study is mostly done in social sciences in which one person, group or event is target for in-depth study. In case study mostly real-life context is studying and researcher try to explore these real-life context with help of case study. Like in this example a 13-year old locked up and studied its ability of language is case study.
