单项选择题

Brain Train
Millions of copies of console and computer- based" brain trainers" are sold worldwide every year, claiming to make peoples’brains younger, better, faster or bigger. The theory seems to make sense: regularly exercising the brain with tests and puzzles can improve brain skills and help people become better at everyday thinking tasks.
But recent research suggests scientific evidence is lacking.
The BBC’s Brain Test Britain experiment wants to find out if brain training really works, and is aiming to get thousands of members of the public to train for 10 minutes a day ,three times a week ,for at least six weeks.
Scientific experiments and their findings should be evaluated by independent experts in a process called "peer review". This is the minimum standard by which the quality of any research is judged.
Very little research on commercial brain trainers has been peer reviewed.
Instead, manufacturers often quote unsupported testimonials from" satisfied users". None of these are acceptable substitutes for peer review.
A proper" control group" is the backbone of any valid scientific study.
With a brain training study, the control group of participants should do the same amount of a mental activity as the brain - training group, but using a" non - brain training" activity such as a crossword.
Scientists should then be able to compare the results from the two groups to see how genuinely effective the brain training tasks were.
Studies that have been used to support the claims made by commercial brain trainers often have no control group at all, or a control group that is not as mentally active as the trained group.
In order to see how much you have improved, you need to know where you were at the start. To do this. scientists use a" benchmarking test"—the same test, taken at the beginning and end of an experiment.
Benchmarking tests should he different from the brain training tasks. This way, scientists can see if the effects of brain training are transferable to other mental tasks.
Studies used to support the claims made by commercial brain trainers often use tests for benchmarking that are identical—or very similar—-to the tests used during training
How do the researchers know the brain -training activity is useful