10% for this disease. Not sure so don't get your hopes up on this answer.
Hope this is going to help you.
They determine it because of the hypothesis. It changes during the investigation and the independent variable stays the same through the whole experiment.
There are no choices given, however, most urban governments have problems with excessive populations leading to excessive amount of trash and other forms of environmental pollution. Though this has been a calculated risk, most urban government planning still lack the responsibility in addressing this environmental concern.