30. Area of the parallelogram formed by the lines $y = m x , y = m x + 1 , y = n x$ and $y = n x + 1$ equals: (A) $| m + n | / ( m - n ) ^ { 2 }$ (B) $2 / | m + n |$ (C) $1 / | m + n |$ (D) $1 / | m - n |$
30. Area of the parallelogram formed by the lines $y = m x , y = m x + 1 , y = n x$ and $y = n x + 1$ equals:\\
(A) $| m + n | / ( m - n ) ^ { 2 }$\\
(B) $2 / | m + n |$\\
(C) $1 / | m + n |$\\
(D) $1 / | m - n |$\\