Which program statement is used to declare a constant in ABAP?

In ABAP, the statement used to declare a constant is "CONSTANTS." This statement allows developers to define a value that cannot be changed throughout the program. Defining constants is useful for maintaining code clarity and preventing accidental changes to values that are meant to remain fixed.

When you declare a constant using this statement, you can assign it a specific value that can be referenced later in the code. Since constants are immutable, they enhance the reliability of the program, as any attempt to alter their value will result in a syntax error during compilation.

Other options like "DATA," "VARIABLES," and "INTERNAL" don’t serve this purpose. "DATA" is used for declaring variables that can change over time, while "VARIABLES" itself is not an ABAP keyword and doesn't apply directly to declaring constants. "INTERNAL" might refer to internal tables or concepts in ABAP having to do with data structures, but again, it is not used for declaring constants. Therefore, "CONSTANTS" is the correct choice for declaring a constant in ABAP.