无法将String[][]中的元素包含在Scala中的单个数据结构中

import scala.collection.mutable.ArrayBuffer

val arrBuffer = ArrayBuffer[String]()

val arr = Array(Array("a", "b"), Array("c", "d"))

for (subArr <- arr) {
  for (elem <- subArr) {
    arrBuffer += elem
  }
}

println(arrBuffer)

import scala.collection.mutable.ListBuffer

val listBuffer = ListBuffer[String]()

val arr = Array(Array("a", "b"), Array("c", "d"))

for (subArr <- arr) {
  for (elem <- subArr) {
    listBuffer += elem
  }
}

println(listBuffer)