Final answer:
The correct answer is option b. Experimental investigation. An experimental investigation would be the best method for Juan to answer the question of whether soil type affects how tall bean plants grow.
Step-by-step explanation:
To answer the question of whether soil type affects how tall bean plants grow, an experimental investigation would be best. In this type of investigation, Juan can set up an experiment in which he grows bean plants in different types of soil and measures their height at the end of the experiment. By controlling other variables such as light, water, and fertilizer, and only changing the soil type, Juan can determine if there is a relationship between soil type and plant height.
For example, Juan can set up three groups of bean plants, each grown in a different type of soil (e.g. sandy soil, clay soil, loamy soil). He can maintain consistent conditions of light, water, and fertilizer for all groups. After a period of time, Juan can measure the height of the bean plants in each soil type and compare the results. If there is a significant difference in plant height among the soil types, then Juan can conclude that soil type does affect how tall bean plants grow.