An international convention regulating trade in endangered species, especially bears and tigers, could be significantly weakened were it not for restrictions on captive breeding of endangered species, warn conservation and animal welfare groups.

(A) could be significantly weakened were it not for restrictions on captive breeding of endangered species, warn conservation and animal welfare groups.
(B) could be significantly weakened if restrictions on captive breeding of endangered species aren't eased, warn conservation and animal welfare groups.
(C) couldn't be significantly weakened without restrictions on captive breeding of endangered species being eased, warn conservation and animal welfare groups.
(D) can't be significantly weakened if restrictions on captive breeding of endangered species are eased, warn conservation and animal welfare groups.
(E) could be significantly weakened if restrictions on captive breeding of endangered species are eased, warn conservation and animal welfare groups.

Can some experts explain the best option?

OA E