An unknown compound (A) has a molecular formula `C_(4)H_(6)`. When (A) is treated with excess of `Br_(2)` a new substance (B) with formula `C_(4)H_(6)Br_(4)`. Is formed (A) forms a white ppt. with ammonical silver nitrate solution. (A) may be,
A. But-1-yne
B. But-2-yne
C. But-1-ene
D. But-2-ene