阅读以下程序片段，判断变量a、b的正确输出结果是（ ）。
int k, a, b; k = 10; a = k + 1; b = k + a; cout << "a = " << a << ", b = " << b;
a = 11, b = 10
a = 11, b = 21
a = 1, b = 10
a = 1, b = 21