Choice B is the correct answer. Doubling implies multiplying by 2.

1. Analyze: "Doubles" means the new value is 2 times the old value.
2. Identify Factor: The multiplier $b$ is 2.
3. Equation: $y = a(2)^x$.

💡 Strategic Tip: "Doubles" $\to b=2$. "Triples" $\to b=3$. "Quadruples" $\to b=4$.

Choice A is incorrect because factor 1 means no change. Choice C is incorrect because 0.5 means halving. Choice D is incorrect because 100 might be confused with 100% growth (which is doubling), but the factor is $1+1=2$.