英语谜语十三 Riddles13

  
11.Why don't babies need glasses?
12.What do you drop when you need it and take back when you don't?
13.What's the difference between a monkey and a flea(跳蚤)?
14.What is black when it is clean and white when it is dirty?
15.What 5-letter word has six left when you take 2 letters away?
16.What is the center of gravity?
17.What never asks questions but always gets answers?
18.When Columbus discovered America,where did he stand?
19.What is four feet on four feet waiting for four feet?
20.When the boy fell into the water,what's the first thing he did?