单选题：h0222. .类ArrayElement定义如下,它的子类定义正确的是？

60.类ArrayElement定义如下,它的子类定义正确的是？

class ArrayElement(val str:String){
def height =1

}











A.class LineElement(str: String) extends ArrayElement{
def width = str.length
}
B.class LineElement(s: String) extends ArrayElement(s) {
def width = str.length
}
C.class LineElement(str: String) extends ArrayElement(str){
def height =1
}
D.class LineElement(s String) extends ArrayElement{
def str = s
}


答案：B