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Directions: In the following questions read the passages carefully and choose the best answer to each question out of the four alternatives. Because goldfish can be kept easily in small ponds and aquariums, they make good pets but like many other pets, they must have proper care and the right kind of place to live. A two-inch fish requires a minimum of two gallons of water containing sufficient oxygen to support life. Some oxygen will make its way into the water of an aquarium from the air that touches the surface. Plants in an aquarium also help to furnish oxygen. Snails help to keep an aquarium clean. Thus, with plenty of plants and snail, the water in an aquarium does not have to be changed frequently. A large lake may prove to be a quite unsuitable abode for goldfish. It is important that goldfish should not be overfed. They can be fed such things as dried insects in addition to commercially prepared goldfish food but they should never be fed more than once a day. Even, then they should not be given more food than can be consumed in about five minutes. This ensures prolonged life.

Water in an aquarium needs to be changed if

A) there are plenty of snails and plants in it

B) there is no sufficient oxygen in it

C) it is very clean and contains sufficient oxygen

D) it does not contain goldfish food and dried insects