It' seems to be strange to you there is a blind spot(盲点 )on the eyes. Here is an interesting experiment（实验） that can make something disappear, when one eye is open.
Make a card about the size of a postcard and write two English letters L and R on it, L on the left and R on the right, First, hold the card about 80 cm away and you see both the letters. Then close your right eye and look at the letter R only with your left eye. And now. as you move the card slowly towards you. you'll find the letter L disappearing. But if you move the card nearer to your face, the letter will be seen again, Now do the same experiment with your left eye closed, you'll find the letter R disappearing,
Why does the letter disappear? It is because there is a blind  spot on the eye. When the　image（影像） or the letter falls on the blind spot, it won't be seen. That is why either of the　letters disappears.
The writer of the passage thinks  that___________ there is a blind spot on the eye.

A．no one knows B．few people know C．most people know D．all the people know

A．遗失 B．驱散 C．消散 D．消失

A．Hold the card B．Move the card nearer C．Write two English letters D．Make a card

A．there is blind spot on the eyes B．a boring experiment C．an interesting story D．when to find the blind spot