Seed habit is the ability to form seeds.
A. Dependent sporophyte is found in Bryophytes and it is dependent on the gametophyte for nutrition.
B. Heterospory is the production of spores of two different sizes and two different development patterns. Small spores are called the male spores or microspores and the larger spores are called female spores or megaspores. Heterospory is an expression of sex determining process of the plants. It is the most important evolutionary development in the vascular plants because it ultimately leads to the seed development.
C. Haplontic life cycle is a primitive type of life cycle which is characterized by zygotic meiosis and haploid adults.
D. Free living gametophyte is the one that does not depend on sporophyte for its nutrition.
Hence, heterospory leads to development of seed habit.
So, the correct answer is 'Heterospory'.