at the low end by zero 如何理解？

Comment 3: Volatility can be measured relative to the current level of rates. By using a lognormal distribution, interest rate movements are proportional to the level of rates and are bounded at the low end by zero.

Which of Annisquam's comments regarding binomial interest rate trees is least likely correct?

选项：

A.

Comment 1

B.

Comment 2

C.

Comment 3

解释：

Correct Answer: A

Annisquam is incorrect in Comment 1. The interest rate tree performs two functions in the valuation process: (1) generating the cash flows that are interest rate dependent and (2) supplying the interest rates used to determine the present value of the cash flows.

请问 at the low end by zero 如何理解？谢谢。