若等差数列\(\{a _{n} \}\)的公差为\(d\)，前\(n\)项和为\(S _{n}\)，记\(b _{n} = \dfrac {S_{n}}{n}\)，数列\(\{b _{n} \}\)的前\(n\)项和为\(T _{n}\)，记\(c _{n} = \dfrac {T_{n}}{n}\)，则\((\:\:\:\:)\)
A.数列\(\{b _{n} \}\)是等差数列，\(\{b _{n} \}\)的公差也为\(d\)
B.数列\(\{c _{n} \}\)是等差数列，\(\{c _{n} \}\)的公差为\( \dfrac {1}{2} d\) C.数列\(\{a _{n} +b _{n} \}\)是等差数列，\(\{a _{n} +b _{n} \}\)的公差为\(2d\) D.数列\(\{a _{n} +c _{n} \}\)是等差数列，\(\{a _{n} +c _{n} \}\)的公差为\( \dfrac {5}{4} d\)
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