Which of the Following Is Not a Rule That Must

Which of the following is not a rule that must be followed when naming identifiers?

A) After the first character, you may use the letters a-z, A-Z, an underscore, a dollar sign, or digits 0-9.
B) Identifiers can contain spaces.
C) Uppercase and lowercase characters are distinct.
D) The first character must be one of the letters a-z, A-Z, an underscore or a dollar sign.