Atheists are defined as:

Atheists are defined as individuals who deny the existence of God. This definition stems from the core principle of atheism, which asserts that there is no evidence or rationale supporting the existence of a deity or deities. The belief system centers around skepticism towards religious claims and often relies on secular and scientific evaluations of existence and morality.

In relation to the other options, those who uphold all religious beliefs would refer to theists, not atheists. Individuals who question the morality of religion may not necessarily reject the existence of a deity; they could still identify as theists while grappling with moral implications within their faith. Finally, those who believe in multiple gods are classified as polytheists, which is distinctly different from the atheistic viewpoint. Thus, the correct answer accurately encapsulates the primary characteristic of atheism.