There are exempted from the computation of the amount of the sales tax the gross receipts from the sale of any tangible personal property to:
(a) The United States, its unincorporated agencies and instrumentalities;
(b) Any incorporated agency or instrumentality of the United States wholly owned by the United States or by a corporation wholly owned by the United States;
(c) The American National Red Cross, its chapters and branches.
(Amended by Stats. 1986, Ch. 308, Sec. 15.)