Why would it be helpful to the police to not have to worry about the fifth amendment protections ?

because they wouldn't have to worry about criminals getting away by using the 5th amendment to their advantage because the 5th amendment protects agains self incrimination

d.prevent the spread of communism outside of eastern europe.

i belive the continental association was created to boycott all contact with british goods.

i also belive it was in december 1, 1774