Final Answer:
D. The ridges of the screw are important because they make it more stable in the wood.
Step-by-step explanation:
The ridges of a screw, also known as threads, play a crucial role in its functionality. Option D is correct because the ridges enhance the stability of the screw in the wood. When a screw is turned into wood, the threads grip the fibers, creating a secure and stable connection. This stability is essential for various applications, such as fastening components together or providing structural support.
In contrast, options A, B, and C are not accurate. Screws do not leave holes in the wood (option A); they create threads within the wood. They are not intended to be bumpy (option B); rather, they should create a smooth and secure connection. Also, the presence of threads makes a screw more stable, not less stable (option C).
Option D is the answer.