Multi-dimensional list

You have the following code:

fun main() {
    val testList = mutableListOf(
        mutableListOf("a", "b", "c", "d", "e", "f", "g"),
        mutableListOf("h", "i", "j", "k", "l", "m", "n"),
        mutableListOf("o", "p", "q"),
        mutableListOf("r", "s", "t", "u", "v"),
        mutableListOf("w"),
        mutableListOf("x", "y"),
        mutableListOf("z")
    )
}

You need to print white. Select letters from testList and arrange them in the correct order top down.