What are the correct factors of (px-py+qx-qy)?

Correct answer: (p+q)(x-y)

Direct answer: B, (p+q)(x-y). Group the terms according to p and q: px-py+qx-qy=p(x-y)+q(x-y). The same bracket, (x-y), is common in both parts. Taking it out gives (p+q)(x-y). Expansion confirms: p(x-y)+q(x-y)=px-py+qx-qy. Option A expands to px+py-qx-qy, so the signs of py and qx do not match. Option C expands to px-pq+xy-qy, which contains the unrelated products pq and xy. Option D expands to pq-py-qx+xy and is also not the given expression. Pay special attention to the minus sign: both terms containing y are negative, so the common bracket must be (x-y), not (x+y). Memory cue: after extracting the common bracket, the remaining outside coefficients are p and q, which therefore combine as p+q.