Answer:
The correct option is;
C. The rate at which the account is increasing
Step-by-step explanation:
The given parameters are;
The rate at which the compound interest on the savings account is compounded = quarterly
The expression given by her banker to find the amount in the account after t years = 4,200(1.05)^(4t)
Therefore, the 1.05 = The rate at which the account is increasing