题目内容：

    Choosing to forget something might take more mental effort than trying to remember it, researchers at The University of Texas discovered. Their findings suggest that in order to forget an unwanted experience, more attention should be focused on it.

“Decades of research has shown that we have the ability to forget something out of our own free will, but how our brains do that is still being questioned. Once we can figure out how memories are weakened and come up with ways to control this, we can design treatment to help people rid themselves of unwanted memories.” said Jarrod Lewis-Peacock, the study's senior author.

Memories are energetic constructions of the brain that regularly get updated, adjusted and reorganized through experience. The brain is constantly remembering and forgetting information—and much of this happens automatically during sleep.

Their findings not only confirmed that humans have the ability to control what they forget, but that successful intentional forgetting requires more activity than what is required to remember.

“A proper level of brain activity is important to this forgetting mechanism (机制). Too strong, it will strengthen the memory; too weak, you won’t change it,” said Tracy Wang, lead author of the study. “Importantly, it's the intention to forget that increases the activation of the memory, and when this activation (激活) hits the “proper level” sweet spot, that's when it leads to later forgetting of that experience”.

The researchers also found that participants were more likely to forget scenes than faces. “We're learning how these mechanisms in our brain respond to different types of information, and it will take a lot of further research before we understand how to use our ability to forget,” said Lewis-Peacock. “Hopefully we can find out how we process and get rid of those really strong memories, which can have a powerful effect on our health and well-being.”

1.What remains a puzzle to researchers?

A.How our memories can be strengthened.

B.How our brains voluntarily forget something.

C.What effect unwanted memories have on our brains.

D.Whether our brains can voluntarily forget something.

2.Which of the following words can best describe memories?

A.Casual. B.Unpredictable.

C.Active. D.Permanent.

3.It can be learned from the text that ______.

A.it requires less attention to forget than to remember

B.the more active the brain is, the faster it forgets

C.humans can't keep memories under control

D.humans forget faces less easily than scenes

4.What can be a suitable title for the text?

A.What It Takes to Forget an Unwanted Experience

B.Strong Memories Have a Great Influence on Health

C.Forgetting Uses More Brain Power than Remembering.

D.How to Train Our Brains to Voluntarily Forget Something