According to Maslow:

A) most people reach the stage of self-actualization during adolescence
B) self-actualization is a well-defined state of happiness and fulfillment
C) higher-level needs will not be tended to until lower-level needs are adequately satisfied
D) higher-level needs always take precedence over lower-level needs

According to Maslow's hierarchy of needs, individuals must satisfy lower-level needs (such as physiological and safety needs) before they can move on to higher-level needs (such as self-esteem and self-actualization). Therefore, option C is correct. Options A, B, and D are all incorrect: A is incorrect because self-actualization is typically reached later in life, not during adolescence; B is incorrect because self-actualization is subjective and varies from person to person, so there is no one "well-defined state of happiness and fulfillment"; and D is incorrect because lower-level needs must be satisfied before higher-level needs can be met.