Read the paragraph and choose the correct idea:

Because goldfish can be kept easily in small ponds and aquariums, they are good pets, but like any other pets, they must have good care and the right kind of place to live. A two-inch fish requires a minimum of two gallons of water containing enough oxygen to support life. Some oxygen will make its way into the water. Plants in an aquarium also help to supply oxygen. Snails help to keep the aquarium clean. Thus, with plenty of plants and snails, the water in an aquarium does not have to be changed frequently. It is important not to overfeed goldfish. They can be fed such things as dried insects and shrimps and commercial goldfish food, but they should never be fed more than once a day. Even then, they should not be given too much food in five minutes.

Which of the following help supply goldfish with oxygen?

• A. 
  Dried insects
• B. 
  Snails
• C. 
  Shrimps
• D. 
  Plants