Which of the following are incomplete ABAP types?

In ABAP, an incomplete data type is one that cannot be used directly to declare variables or structures without providing additional information.

The types 'P' (packed number) and 'C' (character) are valid ABAP data types used for declaring variables. However, packed numbers require specification of their length to be meaningful, making 'P' an incomplete type by itself. For example, a declaration like "DATA: myPackedType TYPE P." would be invalid unless you specify the number of digits, such as "DATA: myPackedType TYPE P LENGTH 10."

On the other hand, 'C' (character) can be used, but if just declared as 'C' without a length (like 'C LENGTH 20'), it is treated as incomplete as well, since it lacks the necessary definition to define its storage size.

The inclusion of 'String' in option D, while typically known as a complete type in newer ABAP versions, is not characterized as an incomplete type in the same sense since it does not require additional parameters for a declaration.

Thus, the option highlighting 'P' and 'C' correctly identifies them as incomplete ABAP types due to their need for specific definitions to be useful.