Final answer:
Normal dry hair is capable of being stretched up to approximately 20% of its length.
Step-by-step explanation:
The correct answer is b) 20%.
Normal dry hair is capable of being stretched up to approximately 20% of its length. This means that if you have a strand of hair that is 10 cm long, it can be stretched to a maximum length of 12 cm.
However, it's important to note that overstretching the hair can cause damage and breakage. It's best to handle hair gently and avoid excessive pulling or stretching.