A cylindrical rotor generator delivers $0.5$ pu power in the steady-state to an infinite bus through a transmission line of reactance $0.5$ pu. The generator no-load voltage is $1.5$ pu and the infinite bus voltage is $1$ pu. The inertia constant of the generator is $5$ MW-s/MVA and the generator reactance is $1$ pu. The critical clearing angle, in degrees, for a three-phase dead short circuit fault at the generator terminal is
1. $53.5$
2. $60.2$
3. $70.8$
4. $79.6$