Which two of the following five physical parameters have the same dimensions ?

Question

(a) Energy density (b) Refractive Index (c) Dielectric constant (d) Young's modulus (e) Magnetic field

$\begin {array} {1 1} (1)\;(a)\: and \: (e) & \quad (2)\;(b)\: and\: (d) \\ (3)\;(c) \: and \: (e) & \quad (4)\;(a) \: and \: (d) \end {array}$