Answer:
C.
Step-by-step explanation:
'At School' is a childhood recollection of Sophie Ruskay of her school days.
In this account Sophie shares that how immigrant children got their schooling and learnt new ways of America by going to school.
The central idea which is presented in the given excerpt is that the immigrant children learnt various facets of America by going to school. They learned about American heroes, folklore, and how American government works. They learned so much about America that when they would leave school, they all seem Americanized.
Therefore, option C is correct.