What does the dup$2()$ system call do$?$

It duplicates a file descriptor in the calling process's file descriptor table. The number assigned to the new file descriptor is specified as a parameter to dup$2().$

It causes the calling process to duplicate itself twice, thereby creating two child processes $($usually for the purpose of sending one child's output to the other child$).$

None of these

It creates two copies of the specified file descriptor in the calling process's file descriptor table. Both of the new file descriptors describe the same object.