Is a set of attitudes, values, and behaviors shared by a group of people?
a etiquette
b diversity
c specialization
d culture

I'm 95% sure it is Culture because culture is things done specifically by a group of people, such as the stated. The other three answers all seem completely off.

I believe the answer is D. I just know its not diversity because they would not have said "shared by a group of people" but instead an individual.

The business cycle is the periodic but irregular up-and-down movement in economic activity, measured by fluctuations in real gross domestic product (gdp) and other macroeconomic variables. a business cycle is typically characterized by four phases—recession, recovery, growth, and decline—that repeat themselves over time. economists note, however, that complete business cycles vary in length. the duration of business cycles can be anywhere from about two to twelve years, with most cycles averaging six years in length. some business analysts use the business cycle model and terminology to study and explain fluctuations in business inventory and other individual elements of corporate operations. but the term "business cycle" is still primarily associated with larger (industry-wide, regional, national, or even international) business trends.