Because (of the need) to maintain the correct balance of salts (and) minerals in the water, (keeping) saltwater fish in aquarium

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问题 Because (of the need) to maintain the correct balance of salts (and) minerals in the water, (keeping) saltwater fish in aquariums requires more work (that) keeping freshwater fish.

选项 A、of the need
B、and
C、keeping
D、that