AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
(C) Single circulation
In fish, blood passes through the heart only once in each circulatory cycle, so it is called single circulation.
The textbook (Chapter 5) states: "blood goes only once through the heart in the fish during one cycle of passage through the body." This is single circulation. Double circulation (option A) applies to birds and mammals, where blood passes through the heart twice per cycle. Options B and D are unrelated concepts.