For $\mathrm{A}\rightleftharpoons \mathrm{B}$ the forward activation energy is $90\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ and $\Delta H=+30\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$. A catalyst lowers the forward activation energy to $70\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$. The activation energy of the reverse reaction in the catalysed route, in $\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$, is

1. A$40$
2. B$60$
3. C$100$
4. D$-10$