Choice A is the correct answer. Compare initial values.

1. Y-intercepts (when $x=0$, $b^0=1$):
   • Function A: $50$
   • Function B: $100$ ← Largest
   • Function C: $25$
   • Function D: $75$
2. Winner: Function B with 100.

💡 Strategic Tip: Y-intercept of $y = ab^x$ is always $a$.

Choice B is incorrect because Function A's intercept is 50, not the largest. Choice C is incorrect because Function D's intercept is 75. Choice D is incorrect because Function C's intercept is only 25.