$5.$ How does exhaust gas recirculation $($EGR$)$ contribute to engine efficiency?

$-$ A$)$ By increasing the engine's power output

$-$ B$)$ By reducing the combustion temperature

$-$ C$)$ By improving the fuel economy

$-$ D$)$ By increasing the air$-$fuel ratio

$6.$ Which characteristic curve would best represent the relationship between engine speed and fuel consumption?

$-$ A$)$ Power Curve

$-$ B$)$ Torque Curve

$-$ C$)$ Efficiency Curve

$-$ D$)$ Fuel Consumption Curve