Pioneer plant species could be described as those that, a) sprout from seeds after a forest fire. b) form large forest trees that shade understory plants. c) are slow to mature, and require a soil with well-balanced nutrients. or d) are small in size, and have highly effective means of dispersing their seeds.

The correct answer is option A, sprout from seeds after a forest fire

Explanation:

Pioneer species are basically the first species that grow or re-originate in any area after a disturbance. Disturbances may include forest fires, floods, etc.  

Here in this questions, in option A, seeds are sprouting after forest fire. Forest fire is a disturbance and seeds sprouting just after a disturbance can be considered as pioneer species of plant.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.