(c) Before the Grand Jury shall enter upon the discharge of their duties the following oath shall be administered to the jurors:
"Do each of you swear (or affirm) that you will diligently inquire into all matters presented to you; that you will return no indictment through malice or ill will, or fail to return one due to fear or reward; and that in all your decisions you will present the truth, the whole truth, and nothing but the truth, according to the best of your skill and understanding. "