What is the sign of the product (−4)(6)(9)(3)?

a) positive, because the products (−4)(6) and (9)(3) are negative and the product of two negative numbers is positive
b) positive, because the products (−4)(6) and (9)(3) are positive and the product of two positive numbers is positive
c) negative, because the product (−4)(6) is negative and the product (9)(3) is positive, and the product of a negative number and a positive number is negative
d) negative, because the product (−4)(6) is negative and the product (9)(3) is negative, and the product of two negative numbers is a negative number