Which of the Following Statements About Significant Digits Are TRUE

Multiple Choice

Which of the following statements about significant digits are TRUE? I.Significant digits are only the digits that are known exactly.
II) Significant digits are all of the digits that are known exactly plus one uncertain digit.
III) Significant digits are a way to communicate the precision of a measurement.
IV) The degree of uncertainty of a measurement is expressed by significant digits.

A) I only
B) II only
C) III and IV only
D) II, III and IV
E) All of the statements are true about significant digits.