Which of the following is true of function templates?
选项：

A: All function templates begin with the keyword class.
B: Every formal type parameter is preceded by either keyword typename or template.
C: Formal type parameters act as placeholders for built-in types or user-defined types and are used to specify the types of arguments to the function, to specify the return type of the function, and to declare variables within the body of the function definition.
D: A programmer must define a separate function template for each template function specialization to be used in the program.