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Solution

Given equation: $xy + yz = 0 \Rightarrow y(x + z) = 0$ This represents two planes: 1️⃣ $y = 0$ 2️⃣ $x + z = 0$ Normal to first plane = $(0,1,0)$ Normal to second plane = $(1,0,1)$ Their dot product = $0(1) + 1(0) + 0(1) = 0$, so the planes are perpendicular. $\boxed{\text{Answer: (D) A pair of perpendicular planes}}$