Choice A is the correct answer. Use the y-intercept to find $k$.

1. Y-intercept: When $x = 0$, $y = k(0.7)^0 = k$.
2. Given: Y-intercept is 140.
3. Conclusion: $k = 140$.

💡 Strategic Tip: For $y = ab^x$, the y-intercept always equals $a$.

Choice B is incorrect because this is the base, not the coefficient. Choice C is incorrect because this is $140 \times 0.7$, the value at $x=1$. Choice D is incorrect because this doesn't match the y-intercept.