Microsoft, after a banner year, gives its 1,600 lead programmer employees an $8,000 bonus. what will be the change in the standard deviation of the employees' income after the bonus is awarded?

Here all employees get equal amount as bonus, so the standard deviation of the employees income won't change. 
if you subtract or add equally to all the data then standard deviation won't change but mean and median would change.

hope this help

Ithink the correct answer is d.