May 1991 Vol. 13, No. 1 8 1,467k May 1991 Vol. 13, No. 2 8 1,322k May 1991 Vol. 13, No. 3 12 1,796k May 1991 Vol. 13, No. 4 12 1,776k May 1991 Vol. 13, No. 5 8 1,583k May 1991 Vol. 13, No. 6 12 2,276k May 1991 Vol. 13, No. 7 8 1,446k May 1991 Vol. 13, No. 8 8 1,423k May 1991 Vol. 13, No. 9 8 1,210k June 1991 Vol. 13, No. 10 8 1,439k June 1991 Vol. 13, No. 11 16 2,826k June 1991 Vol. 13, No. 12 8 2,252k June 1991 Vol. 13, No. 13 8 1,329k