Step 1: Understanding the Question:
This question tests knowledge of light conditions under forest canopies.
Step 2: Detailed Explanation:
Seedlings growing under a forest canopy receive partially exposed light.
They receive some sunlight filtered through the canopy.
Totally exposed (A): Not under canopy.
Thick canopy (C): Receives very little light.
Thin canopy (D): Receives more light.
Thus, the correct answer is partially exposed.
Step 3: Final Answer:
Thus, seedlings under canopy receive partially exposed light, which corresponds to option (B).
[0.5cm]