What is the switch that is used to make sure that the copy command copied files correctly

The /v switch is used with the copy command in DOS to verify that files are copied correctly.

When you use copy /v, DOS verifies each file after copying to ensure that it matches the original file.
This switch is useful for ensuring data integrity during file copying operations.
If any discrepancies are found during verification, DOS displays an error message.

/a switch is used with the copy command to copy files with the archive attribute set, but it does not verify the copy.

/c switch is not used with the copy command in DOS for verifying file copies.

/s switch is used with the copy command to copy directories and subdirectories, not for verifying file copies.

Therefore, the correct answer is Option D: /v.