Hello everyone ,
 
I would be grateful if anyone could help me in the following :
 
Which is more correct in changing the following sentence into the impersonal passive form :
 
People think that we only use a small percentage of our brain power .
It can be done as follows :   
 1.  It is thought that we only use a small percentage of our brain power .
2. Only a small amount percentage of brain power  is thought to be used  . OR Only a small amount percentage of brain is thought to use      OR   what ?????????//
 
Another sentence :
 Experts have proved that exercise is good for concentration .
 Which possibility is correct :
1. It has been proved that exercise is good for concentration . OR it is proved that exercise is  good for concentration  .
 
 
 THANKS ALL