Final answer:
The name 'sysver' is not a valid user-defined macro variable because it is likely a system reserved name, possibly representing the version of the software. Other options like 'month', '_year', and 'total_sales' are generally acceptable user-defined macro variable names.
Step-by-step explanation:
Among the options given, c. sysver is NOT a valid name for a user-defined macro variable. When creating macro variables in programming environments such as SAS, there are naming conventions that must be followed. Typically, a user-defined macro variable cannot have the same name as a system reserved macro variable. The name 'sysver' suggests it could be shorthand for 'system version' which is likely to be a reserved name in many systems because it could denote the version of the software in use. Thus, it is not recommended to use 'sysver' as it may conflict with system-defined variables.
Other names like 'month', '_year', and 'total_sales' are generally acceptable as they do not start with 'sys' which could be a prefix reserved for system-related macro variables in many programming environments. Remember to always check the specific language documentation for reserved keywords and conventions.