If $k=\frac{a+b}{a b}$ is a non-zero constant, then the point which lies on the straight line $\frac{x}{a}+\frac{y}{b}=1$ is
- A
$(k, k)$
- B
$\left(k, \frac{1}{k}\right)$
- C
$\left(\frac{1}{k}, k\right)$
- D
$\left(\frac{1}{k}, \frac{1}{k}\right)$
✓ Correct answer: D
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