If `m`
parallel
lines in a plane are intersected by a family of `n`
parallel
lines, the number of parallelograms that can be formed is
a. `1/4m n(m-1)(n-1)`
b. `1/4m n(m-1)(n-1)`
c. `1/4m^2n^2`
d. none of
these
A. `((m-1)(n-1))/(4)`
B. `(mn)/(4)`
C. `(m(m-1)n(n-1))/(2)`
D. `(mn(m-1)(n-1))/(4)`
