趣味问答。

1. Ten plus ten is ten. Ten minus ten is ten. What am I?                 

2.  I have two feet.  I can walk(走路).  And I can tell you the time.

     What am I?                   

3.  Peter's father isn't at home today.

         Things (东西) are at sixes and sevens.                  

4. They go to the zoo in ones or twos.                 

下列哪种方法可以用来直接检验概念形成中所采用的假设（）

A.人工语法实验

B.空白实验

C.人工概念实验

D.扫描实验