Match the sum formulas$S_n$ with the indicated sequences $a_n$. They are to hold true for all positive integers $n.$

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1.  $a_n = 3n-2$   2.  $a_n = 3n-1$   3.  $a_n = 5^{n-1}$   4.  $a_n = n^2$

A.  $\displaystyle S_n = \frac{n(3n-1)}{2}$ B.  $\displaystyle S_n = \frac{5^n-1}{4}$ C.  $\displaystyle S_n = \frac{n(3n+1)}{2}$ D.  $\displaystyle S_n = \frac{n(n+1)(2n+1)}{6}$

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