Question

read the paragraph, then choose the word that best completes the sentence.
how can you tell when fish are sick? veterinarians at aquarium of the pacific say that you just have to watch them. they do not cry, cough, or run a fever. a sick fish, for example, might rub against rocks. this tells the caretakers the animal is itchy from a skin problem. some fish gain weight when they are sick. others move around less than before. surprisingly, fish breath can tell caretakers a lot. some bad breath is normal in fish. often, this is because fish eat other fish and have bacteria in their mouths. but really bad breath can be caused by sickness or disease.
the caretakers look for ______ signs.
a troubling
b regular
c friendly
d appealing

Explanation:

The paragraph is about how to tell when fish are sick. The signs mentioned (rubbing against rocks, weight gain, less movement, really bad breath) are all negative or concerning things related to sickness. "Troubling" means causing concern or worry, which fits these signs. "Regular" means normal, which doesn't match as these are not normal healthy signs. "Friendly" has nothing to do with the context of fish being sick. "Appealing" means attractive, which is also not relevant to the signs of sick fish.

Answer:

A. Troubling