The Earthly Branch paired with the Horse in the Chinese zodiac is Wu, written 午 in Chinese.
The Earthly Branches are a cycle of twelve symbols used with the ten Heavenly Stems in the traditional sexagenary calendar. Each branch is also associated with a zodiac animal. 午 is the seventh branch and corresponds to the Horse, making “Wu” the expected Mandarin romanization.
The branch has meanings beyond the animal cycle. 午 is linked with yang energy, the Fire element, the southern direction, and the midday period, traditionally around 11 a.m. to 1 p.m. These associations come from the wider calendrical and cosmological system rather than from the zodiac animals alone.
Several answer choices are branches associated with other animals: Zi (子) is the Rat, Mao (卯) is the Rabbit, and You (酉) is the Rooster. Romanization can vary across languages, but “Wu” is the conventional Mandarin spelling used in English-language references.