1是第一个程序； 2是第二个程序。
1a. i should reach at 0;
1b. x = null, y = 1;
1c. x = [2, 3, 5], y = 3;
1d. x = [2, 3, 5], y = 1;
2a. it just finds the first 0;
2b. x = null;
2c. x = [0];
2d. x = [1, 0, 1].