Which command is used to make all files and sub-directories in the directory (progs) executable by all users?

In Unix, the chmod command is used to change the permissions of files and directories. The -R option is used to recursively change permissions for the specified directory and its subdirectories. The a+x part of the command grants execute permission to all users (owner, group, and others). So, chmod -R a+x progs makes all files and subdirectories in the progs directory executable by all users.
Therefore, Option A is the correct command to achieve the desired task.