Which of the following produces embryo sac?

The correct option is B Megaspore

A diploid Megaspore mother cell is developed inside the nucellus. It then undergoes meiotic division to form four haploid megaspores. Out of these four megaspores, three degenerate and only one remains functional. This functional megaspore then undergoes mitosis three times without cytoplasmic divisions which results in 8 nuclei in the megaspore. These 8 nuclei then get organized into egg apparatus (consisting of an egg cell and two synergids) at micropylar pole, a large central cell in the centre and three antipodal cells at chalazal pole. This results in the formation of a 7-celled but 8-nucleate structure which is called the embryo sac.

Hence, it's the functional megaspore that develops into embryo sac. So, the correct answer is B.