单选题 下列程序段的输出结果是int main(void){ int m, k = 0, s = 0; for (m = 1; m <= 4; m++) { switch (m % 4) { case 0: case 1: s += m; break; case 2: case 3: s -= m; break; } k += s; } printf("%d ", k); return 0;}