执行以下代码后的结果是（ ）

int grade = 80;
switch (grade / 10) {
    case 10:
    case 9:
        cout << "A";
        break;
    case 8:
    case 7:
        cout << "B";
        break;
    case 6:
        cout << "C";
        break;
    default:
        cout << "D";
}