plz help me

Welcome to Using English

Mr. = Mister - A male, married or unmarried. (The old "Master" for boys is not used any longer.)
Mrs. = (pronounced) Missuz. No one uses "Mistress" any longer.
Miss is exactly that - Miss. An unmarried woman.
Ms. = (pronounced) Miz. A woman whose marital status is not known or who chooses to be called this. Both married women and single women choose to

thank you......."Medical and Dental English" It's mistake : ))

Well "mistress" is still used, but not in the way you're thinking

True enough. But don't say "Here comes Mister Jones, and this must be his charming mistress we have heard so much about." At least, don't say that if you like Mr. Jones.