The maize grain is regarded as a fruit and not a seed because

Explanation

Maize grain is an important staple food in many parts of the world. The question asks why maize grain is considered a fruit and not a seed. The options are given as A, B, C, and D. The correct answer to this question is B: the testa and fruit wall fuse after fertilization. Maize grain is considered a fruit because it develops from the ovary after fertilization. The ovary is the part of the flower that contains the developing ovules, which later become seeds. In the case of maize, the ovary grows into a large structure called a cob, which is covered by leaves that form a sheath around it. Each kernel of maize is actually a fruit, with a single seed inside. The structure of the maize fruit is different from that of typical seeds. In a typical seed, the seed coat is distinct from the fruit wall, and the two structures do not fuse together. In maize, however, the fruit wall and the testa (the outer layer of the seed coat) fuse together after fertilization, forming a single structure that encloses the developing endosperm and embryo. This is why maize is considered a fruit rather than a seed. In summary, maize grain is considered a fruit because it develops from the ovary after fertilization, and the fruit wall and testa fuse together to form a single structure that encloses the seed. The correct answer to the question is B: the testa and fruit wall fuse after fertilization.