What can cause split nails?

Split nails can result from multiple factors that damage the structure and integrity of the nails. Injury is a common cause; trauma to the nail can lead to splits or cracks. Improper filing practices can also contribute to splitting, as aggressive or incorrect filing techniques can weaken the nail's structure. Additionally, harsh chemicals, such as those found in certain cleaning products or nail polishes, can strip the nails of essential moisture and proteins, making them brittle and more susceptible to splitting.

Choosing "B" recognizes that split nails can occur due to a combination of these factors, emphasizing the importance of healthy nail care practices. Each of the other options identifies a specific cause, but the correct answer encapsulates the broader view that multiple sources can lead to the same outcome of split nails.