Final answer:
Hardcore featured slam dancing and mosh pits, remained largely underground with little mainstream success, and developed in different US regions simultaneously, each with a unique style. Therefore, the correct option is B.
Step-by-step explanation:
Of the statements regarding hardcore, option 'b' is true: Slam dancing and mosh pits were features of this style. Hardcore, a subgenre of punk rock that emerged in the late 1970s and early 1980s, was characterized by faster tempos and more aggressive playing styles compared to the original punk rock movement. Option 'd' is also true as hardcore typically remained underground with limited mainstream commercial success. It tended to resist the commercialization that punk rock experienced. Regarding 'e', hardcore did develop roughly simultaneously in various regions of the United States, including both coasts, but with local scenes having their distinct styles and influences.