contraction ,abbreviation的区别?

Contraction:A word,as won't from will not,or phrase,as o'clock from of the clock,formed by omitting or combining some of the sounds of a longer phrase。Abbreviation:A shortened form of a word or phrase used chiefly in writing to represent the complete form,such as Mass。for Massachusetts or USMC for United States Marine Corps。Acronym:A word formed from the initial letters of a name,such as WAC for Women's Army Corps,or by combining initial letters or parts of a series of words,such as radar for radio detecting and ranging。