Dolphins are mammals and sharks are fish. they both have fins. this suggests that

dolphins and sharks inherited fins from a recent common ancestor

both dolphin and shark fins are vestigial features

dolphin and shark fins are analogous structures

a dna mutation caused some sharks to evolve into dolphins

I believe  that it is dolphin and shark fins are analogous structures

americans began to notice growing differences between the northern and southern sections of the country. there were more people living in cities in the north, which made it more urban. more people lived on farms in the south, which made it more rural. while many people were farmers in the northern states, there were now other ways to make a living, such as working in mechanical cotton gins factories manufacturing cloth, tools and other goods. people in the north supported high tariffs on goods imported from europe because the extra cost encouraged people to “buy american” instead. in the southern states, planters did not like tariffs because they sold most of their production to europe and bought their tools from there as well. southerners believed the protective tariff was something that only northern factory owners keep their profits high. so the southern politicians came up with an idea. they would opt out. they would simply ignore the protective tariff. it was ‘null and void’ in south carolina. the state would not collect the taxes on goods imported into south carolina, no matter what the president said they had to do. this decision led to the nullification crisis.

true, i don't really know what you're asking but from the info you provided im guessing the answer is true.