Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason \(R\). Assertion A : Efficiency of a reversible heat engine will be highest at \(-273^{\circ} C\) temperature of cold reservoir. Reason \(R\) : The efficiency of Carnot's engine depends not only on temperature of cold reservoir but it depends on the temperature of hot reservoir too and is given as \(\eta=\left(1-\frac{ T _2}{ T _1}\right)\). In the light of the above statements, choose the correct answer from the options given below

1. A \(A\) is true but \(R\) is false
2. B Both \(A\) and \(R\) are true but \(R\) is NOT the correct explanation of \(A\)
3. C \(A\) is false but \(R\) is true
4. D Both \(A\) and \(R\) are true and \(R\) is the correct explanation of \(A\)