How do tax policies promote the interests of particular groups or encourage specific activities? how do tax expenditures amount to government subsidies for different activities? give specific examples

Taxation can help the activities of a particular group in the sense that they limits competition or encourage it whether it is a producer or consumer groups.
 tax expenditure amount to subsidy because they lead to exemptions or deductions and reduction of credits targeted to a particular  or specific group, for example medicare.

The bystander effect  for some reason my history teacher was talking about this 

Like many students at university, you may be unhappy about the results you attain in exams. you may feel that even with all you are doing there must be something more -- or different-- you could be doing to get better grades. we have all at some time or other heard of that student who only studies a couple of hours for final exams and scores a's every time. we stand in awe of those who seem to breeze through without undue effort and seem to need very little in the way of studying to nail an exam. the reasons for success, in what i think are the vast majority of cases, are less esoteric than many students think: successful students consistently apply a series of productive strategies with view to attaining clearly identified learning and grade goals throughout the academic term.