an arithmetic sequence is a sequence in which you use addition/subtraction in order to achieve each term. Choice A alternates between the negative and positive therefore you can tell that it's multiplying each time, and the same goes for D, those two are incorrect. B is incorrect because you cannot add/subtract a number each time to get the next term. C, if you attempt to find the difference between in each term in choice C you will succeed and find that each time you add 3/2 each time to get the next term.
