A thermometer indicates \(-50^{\circ} \mathrm{C}\) and \(70^{\circ} \mathrm{C}\) at the lower and upper fixed points respectively. What temperature does the thermometer register when the true temperature is \(66.7^{\circ} \mathrm{C}\) ?
A. \(80^{\circ} \mathrm{C}\) B. \(50^{\circ} \mathrm{C}\) C. \(30^{\circ} \mathrm{C}\) D. \(20^{\circ} \mathrm{C}\)