✔ 最佳答案
for example,when you get a pencil on the left,it is always on the left.if it doesn't work,if you get a pencil from the right,next,pick the one in the middle,then left ,then right.....if it does't work,try the opposite-if you get a pencil from the right,next,pick the one in the left,then middle,then right,then left.....