算不出这数

问题如下：

Suppose that we have the following data on three features for each of three banks, A, B, and C:

Scale the features using standardization. What is the standardized number of customers of Bank A ?

选项：

A.

-0.690

B.

-0.456

C.

-0.666

D.

-0.498

解释：

As an example, undertaking the standardization for bank A and the customers feature, the calculation would be:

(1.2 - mean(1.2,6,0.5)) / std(1.2,6,0.5) = -0.456.