Which of the Following Is Generally Not True of Witnesses

Which of the following is generally not true of witnesses and their testimony?

A) Witnesses provide evidence in the form of testimony to help the triers of fact better ascertain the truth.
B) Witness testimony may be from personal knowledge or from what the witness has heard from a reliable source.
C) Witnesses are also called to lay a foundation for other evidence being offered, to identify and authenticate this evidence.
D) Some types of witnesses are allowed to offer their opinions as to how certain evidence was obtained or what it means