U$.$S business entities are taxed according to one of three basic sets of rules $(1)$ separate legal entity, flow$-$through, or the $$either$/$or$$ approach. $($For this question, you may ignore the $$quasi$-$flow$$ approach, which approximates $$flow$-$through$$ taxation$).$ Explain how entity income is taxed under each approach, and when each approach is applicable $($which business entities are taxed under each approach$).$