#### Answer

(a) negative
(b) positive
(c) positive
(d) negative

#### Work Step by Step

(a) Since a is positive, -a is negative.
(b) Since b and c are both negative, bc is positive.
(c) Since a is positive and b is negative, a-b is positive (subtracting a negative number reverses the sign and this essentially becomes the sum of two positive numbers, which is positive).
(d) Since a is positive and b is negative, ab is negative. Similarly, since a is positive and c is negative, ac is negative. Thus ab + ac becomes the sum of two negative numbers, which is negative.