Javascript"；变量"；没有定义

我编写了一个脚本，从用户那里获取不同单位的分数，然后将它们添加到数组中，显示分数和平均值

当我运行脚本时，它工作正常，但它显示的不是平均值，而是未定义的“grade”

var subjects = ["CF:", "DaD:", "PoP:", "N&CS:", "SAD:", "APP:"];
var grades = ["", "", "", "", "", ""];
var result;

grades[0] = prompt("Please enter your marks for CF: ");
grades[1] = prompt("Please enter your marks for DaD: ");
grades[2] = prompt("Please enter your marks for PoP: ");
grades[3] = prompt("Please enter your marks for N&CS: ");
grades[4] = prompt("Please enter your marks for SAD: ");
grades[5] = prompt("Please enter your marks for APP: ");


console.log("Units and grades are: ");

console.log(subjects[0] +"\t"+ grades[0] );
console.log(subjects[1] +"\t"+ grades[1] );
console.log(subjects[2] +"\t"+ grades[2] );
console.log(subjects[3] +"\t"+ grades[3] );
console.log(subjects[4] +"\t"+ grades[4] );
console.log(subjects[5] +"\t"+ grades[5] );

result = grades[0] + grades[1] + grades[2] + grades[3] + grades[4] + 
grade[5];

console.log("Average: " +  "\t" + result / 6);

有人有什么想法吗？ 为糟糕的javascript致歉，我对此很陌生。

在这段代码中

result = grades[0] + grades[1] + grades[2] + grades[3] + grades[4] + grade[5];

---

等级[5]必须是等级s[5]。你错过了“s”点。

在

result=…

一行输入错误：

grade[5]

。我是个十足的白痴，谢谢。