We usually believe what our brain tells us, but there are some amazing facts which show that the brain tricks us. As a result, we think we can see something that is not actually there or we ignore（忽视）things that actually are there.
Scientists Daniel Simons and Christopher Chabris have researched this phenomenon（现象）, which they call “change blindness”. Their experiments show how we sometimes just do not see what is in front of our eyes because                      .
Here is one of their most famous experiments. In this experiment, the participants（参与者）were shown a video of two groups of people (one group in white T-shirts and one group in black T-shirts) who passed basketballs around in a hallway. Each group had three members. Simons and Chabris asked the participants to count how many times the white team passed the ball. While the two teams were passing their balls around, a person dressed up as a big bear walked through the group and stopped to look at the camera. Simons and Chabris found that about half of the research participants did not notice the big bear.
What do Daniel Simons and Christopher Chabris do?

A．Scientists.

B．Astronauts.

C．Engineers.

D．Directors.

How many people did the experiment need in the video?

A．Three.

B．Four.

C．Six.

D．Seven.

What percentage of the participants noticed the big bear? 

A．Less than 25%.

B．About 50%.

C．About 75%.

D．Almost 100%.

Which is the most suitable to complete the last sentence in the second paragraph?

A．we are not interested in it

B．we are too confident to see it

C．we are depending on other people

D．we are paying attention to watching something else