The correct option is C an=1a+(n−1)d
Given, a and d are the first term and the common difference of the A.P.
∴a,a+d,a+2d,........,a+(n−1)d forms an AP.
Since, if a,b,c are in AP. then 1a,1b,1c are in HP.
∴1a,1a+d,1a+2d,........,1a+(n−1)d are in HP.
∴ nthterm of HP =an=1a+(n−1)dOption B is correct.