The answer to this question should be A for the following reasons:

1. Like the one above, the sturgeon is a real thing and the mermaid is illusory, so B is excluded;

2. As above, sturgeons and mermaids are related, so C is excluded;

3. Only A and D are left.

Mermaids are in legends, and unicorns are also in legends.

Baidu Encyclopedia’s explanation of “unicorn” says: “There are legends about unicorns in both China and the West. Unicorns in Chinese mythology are auspicious animals that only appear when fulfilling important missions. There are about 6 forms of unicorns, the more famous one is the unicorn. The Western unicorn is shaped like a white horse with a spiral horn on its forehead, which represents nobility, pride and purity."

It can be seen that " The definition of "unicorn" is much larger than that of "unicorn". At the same time, "mermaid" is derived from foreign legends, and the term "unicorn" also belongs to foreign countries (because China calls it "unicorn"). According to the principle of analogy, it should be foreign to foreign.

Therefore, question A is more in line with the meaning of the question.