Study the following and identify the correct statements.
I) Both exonucleases and endonucleases cleave phosphodiester bonds.
II) Restriction endonucleases act on sugar phosphate  back bone of DNA helix and break phosphodiester bonds bonds.
III) When two different DNA fragments are cut by same restriction endonuclease enzyme the resultant fragments do not have same kind of sticky ends.
IV) All enzymes that belong to class nucleases are restriction endonucleases.