Why is the development of seeds considered to be important for the evolution of land plants from spore-bearing vascular plants?

Seed is important for the evolution of land plants from spore-bearing vascular plants because it contains already fertilized ovule (embryo) duly protected and nourished by the seed coat.

Explanation:

Spore bearing vascular plants are often confined to wet/damp habitats because water is needed for sexual reproduction and completion of their life cycle in most cases. They also need to produce a large amount of spore in order to be successful because the spores are easily lost to unfavourable environmental conditions.

In order for plants to be adapted and be able to successfully propagate on dry land, the problem of water-for-fertilization needs to be tackled. This is why the development of seeds is important for the evolution of land plants.

A typical seed carries an already fertilized ovule in the form of embryo. This embryo is well protected and in continuous nourishment by the seed coat. With this, the water requirement for fertilization is completely eliminated and the embryo can survive a wide range of environmental conditions over a considerable time. Unlike spores, seeds can be dispersed over a relatively long distance using several means

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.