(d) 40°
By SSS similarity, △ABC ~ △RQP (since AB/RQ = BC/QP = CA/PR = 1/2). So ∠C = ∠P. In △PQR, ∠P = 180° − 80° − 60° = 40°, therefore ∠C = 40°.
This is directly from Example 5 of the textbook (Chapter 6, Section 6.4). The key step is identifying the correct correspondence: A↔R, B↔Q, C↔P. Once △ABC ~ △RQP is established by SSS, ∠C corresponds to ∠P, and ∠P is found by the angle sum property. Examiners expect you to state the similarity criterion and the correct symbolic form of similarity.