Final answer:
Gender is the classification that is not considered a suspect classification for equal protection purposes; it is subject to intermediate scrutiny rather than strict scrutiny.
Step-by-step explanation:
When a law or government action classifies persons based on a suspect classification, strict scrutiny is the standard used to determine if it violates the Equal Protection Clause. Suspect classifications generally include those based on race, alienage, national origin, and religion; these are classes that have historically faced significant discrimination. However, discrimination based on gender is analyzed under a different, lesser standard known as intermediate scrutiny. Unlike strict scrutiny, which requires a compelling state interest and the law or action to be narrowly tailored to achieve that purpose, intermediate scrutiny requires the government to show that different treatment is substantially related to an important governmental objective.
The correct answer to the question, which asks which of the following is not a suspect classification for equal protection purposes is Gender (D).