For each of the integrals below, decide (without calculation) whether the integrals are positive, negative, or zero. Let $D$ be the region inside the unit circle centered on the origin, $R$ be the right half of $D$, $L$ be the left half of $D$, $B$ be the bottom half of $D$.

(a) $\int_{R} (2 y^3 + y^5)\, dA$ is ? positive negative zero

(b) $\int_{L} 2 x\, dA$ is ? positive negative zero

(c) $\int_{B} (2 y^2 + y^4)\, dA$ is ? positive negative zero

(d) $\int_{R} (2 x^2 + x^4)\, dA$ is ? positive negative zero