What Does It Mean If an Ellipsis, or Three Dots

What does it mean if an ellipsis, or three dots (i.e. '…') , appears in the middle of a quotation?

A) There is a mistake in the quotation (spelling or grammar, for example) that was in the original. The ellipsis is used to show that the error was in the original and was not made by the person reproducing the quotation.
B) That additional material has been added to the quotation that was not in the original. This may be done to help the quote work if it is part of a sentence.
C) Material has been omitted from the original quotation. This may be used to save words or to ensure that the reader is not distracted by irrelevant material in the quotation.
D) It is used to add emphasis that is not in the original quotation.