VBS二维数组之间相互赋值

在VBS里如何把a数组的某个元素给b数组不会出现下标越界的问题？（两个数组都是二维数组）

取值赋值之前先判断下标是否越界

Dim a(1 To 2, 1 To 3) As Variant
a(1, 1) = "a"
a(1, 2) = "b"
a(1, 3) = "c"

Dim b(1 To 1, 1 To 3) As Variant
b(1, 1) = a(1, 1)