the signs on the wall means 'no littering'.对 on the wall 提问 悬赏80财富- -急

问题描述:

the signs on the wall means 'no littering'.对 on the wall 提问 悬赏80财富- -急
急 刚刚那个人的同学- -同一张试卷

Which signs means 'no littering'?
补充:你肯定觉得奇怪,为什么对地点提问,而不用Where提问,因为这里的on the wall意思是“墙上的”,而不是在墙上.类似举例:
The girl in the boat is my sister.(对in the boat提问):Which girl is your sister?
赠人玫瑰,手留余香!——福来美Flower Magic
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