The Author of This Study Refers to the Term "Flexible

The author of this study refers to the term "flexible ethnicity." What does she mean by this?

A) Today, people are of so many mixed races that we can be flexible in what we call them and how we refer to their heritage.
B) It refers to the idea that we can navigate different racial terrains and can be an "insider" in more than one ethnic group.
C) There are very strict boundaries about ethnic identities, and we have to be very careful in how we relate to and call people in terms of their cultural heritage.
D) With a larger percentage of people engaging in inter-racial marriages, there is much more elasticity about racial designations than ever before.