The first langauge L1 necessitates that d should follow c and no of c = no of d..And the second langauage L2 says that no of a's and b's should be equal.
In both of the languages , the sequence is a's followed by b's followed by c's and then d's..
But considering the requirement of L1 and L2 , we need that no of a's = no of b's and no of c's = no of d's ..However no constraint between no of a's and no of c's or no of b's and no of d's..
Hence the language L1 ∩ L2 = { an bn cm dm | m,n >= 0 }
Hence D) is the correct answer