X melts at a higher temperature than P melts. Y melts at a lower temperature than P melts, but at a higher temperature than Q melts. If the statements above are true, it can be concluded with certainty that S melts at a higher temperature than Y melts, if one knows in addition that

Explanation: (C) From the given statements: \(P < X\); \(Q < Y < P\). Combining these, the order of melting temperatures is \(Q < Y < P < X\). To conclude that \(Y < S\), we need information about S relative to Y, P, or X. If we know \(P < S\), then since \(Y < P\), it must be true that \(Y < P < S\), or \(Y < S\). Thus, "P melts at a lower temperature than S melts" is sufficient.