The Primary Purpose of a Witnesses Who Appear in Criminal

The primary purpose of a witnesses who appear in criminal cases is:

A) usually not too important because the jury has the primary role of deciding the case, not the witness.
B) to present evidence to the court and jury.
C) to evaluate the testimony of the other witnesses.
D) to give oral testimony, but a witness may not introduce real or documentary evidence into court unless qualified as an expert witness.