File with which extension is not executable?
Exe is obviously executable. Executable means the instructions inside the file are loaded into memory and processor runs those instructions.
Com is the extension for command file. It is similar to the exe files. The thin difference is that EXE contains programs while COM contains commands only.
Bat is the extension of for a DOS file that contains a batch of user written commands. If there is certain set of commands you need to run repeatedly, you can automate the task by creating BAT file. Thus, it is also executable file.
SYS is the extension for system files. These files contains configurations, not commands to execute. The programs and commands will refer to these files to check what the permitted values are while they run various tasks. This file is not executed, just loaded and kept ready for any other programs or commands to refer.
So, option C is the correct answer.