Which of the following statements about free radical halogenation of alkanes are correct? (Use the bond dissociation energies: primary C-H 101 kcal/mol, secondary C-H 98.6 kcal/mol, H-Cl 103 kcal/mol, H-Br 87.5 kcal/mol.)

1. ABromination of 2-methylpropane gives mainly 2-bromo-2-methylpropane
2. BChlorination is more selective than bromination between tertiary and primary C-H bonds
3. CHydrogen abstraction from a secondary C-H by $\mathrm{Br}\cdot$ is endothermic
4. DHydrogen abstraction from a primary C-H of propane by $\mathrm{Cl}\cdot$ is exothermic