The correct answer is option 1: soil, water, and temperature. The distribution of characteristic vegetation in a region is primarily determined by these factors.

Soil plays a crucial role in determining the availability of nutrients and water retention capacity, which directly affects the types of plants that can grow in an area.

Water availability is another vital factor. Plants require water for their growth and survival. Regions with abundant rainfall or proximity to water bodies may have different types of vegetation compared to arid regions.

Temperature influences the growth and adaptation of plants. Different plants have specific temperature requirements, and extreme temperatures can limit the distribution of certain species.

While options 2, 3, and 4 also include significant environmental factors, they are not the primary factors determining the distribution of characteristic vegetation.