What is the chief product obtained when `n-`butane is treated with `Br_(2)` in the presence of light at `130^(@)C`?
A. `CH_3-CH_2-underset(underset(CH_3)|)CH-Br`
B. `CH_3-underset(underset(CH_3)|)CH-CH_2-Br`
C. `CH_3-underset(underset(CH_3)|)overset(overset(CH_3)|)C-Br`
D. `CH_3-CH_2-CH_2-CH_2-Br`