The cactus is now heavily plundered in deserts in the southwestern United States, so much that enforcement agencies in five states have created special squads for its protection.


(A) The cactus is now heavily plundered in deserts in the southwestern United States, so much that enforcement agencies in five states have created special squads for its protection.

So much that is not the correct idiomatic usage. 

It should be- so heavily plundered (cause)..that the agencies .. (effect)


(B) The cactus is now heavily plundered in deserts in the southwestern United States, so much so that special squads have been created by law enforcement agencies in five states for protecting them.

The cactus is singular and cacti is plural.

Therefore we eliminate option

The plural pronoun “them” cannot be use for the singular noun- cactus. 


(C) The cactus is now so heavily plundered in deserts in the southwestern United States that enforcement agencies in five states have created special squads to protect it.

So X that Y is the correct usage. The pronoun “it” refers to the singular noun- cactus. 


(D) Because they are now so heavily plundered in deserts in the southwestern United States, enforcement agencies in five states have created special squads to protect cacti.


“Because they are now so heavily plundered” incorrectly modifies “enforcement agencies.” 


(E) Because they are now so heavily plundered in the southwestern United States, special squads have been created by enforcement agencies in five states for the protection of cacti. 


“Because they are now so heavily plundered” incorrectly modifies “special squads.”