Hana deposited a fixed amount into her bank account each month. The function f t =

Choice A is correct. It's given that $t$ represents the number of monthly deposits. In the given function $f\left(t\right)=100+25t$, the coefficient of $t$ is $25$. This means that for every increase in the value of $t$ by $1$, the value of $f\left(t\right)$ increases by $25$. It follows that with each monthly deposit, the amount in Hana's bank account increased by $\$25$.

Choice B is incorrect. Before Hana made any monthly deposits, the amount in her bank account was $\$100$. 

Choice C is incorrect. After $1$ monthly deposit, the amount in Hana's bank account was $\$125$. 

Choice D is incorrect and may result from conceptual errors.