Let \( S \) be the set of all the natural numbers, for which the line \( \dfrac{x}{a}+\dfrac{y}{b}=2 \) is a tangent to the curve \( \left(\dfrac{x}{a}\right)^{n}+\left(\dfrac{y}{b}\right)^{n}=2 \) at the point \( (a,b), ab\neq 0 \). Then:
\( S=\phi \)
\( n(S)=1 \)
\( S=\{2k:k\in N\} \)
\( S=N \)
