Two glass bulb $A$ and $B$ are connected by a very small tube of negligible volume having stopcock. Bulb $A$ has a volume of $100 cm ^{3}$ and contains a certain amount of gas while bulb $B$ is empty initially, with stopcock closed. On opening the stopcock for considerable time period, the pressure in A fell down by $60 \%$. The volume of bulb B must be : (Assume temperature to remain constant)
(A) $200 mL$
(B) $150 mL$
(C) $250 mL$
(D) $100 mL$
