Find the value of

`( a^( m^2 - n^2 ))^ (( m^2 + mn + n^2 )/( m + n )) times ( a^( n^2 - p^2 ))^ (( n^2 + np + p^2 )/( n + p ))times ( a^( p^2 - m^2 ))^ (( p^2 + mp + m^2 )/( p + m ))` is

( a ) 0   ( b )   1   ( c )   `a^3`   ( d )   a