Final answer:
The fourth section of the Liber Abaci describes mathematical puzzles and riddles.
Step-by-step explanation:
The fourth section of the Liber Abaci describes a) Mathematical puzzles and riddles. The Liber Abaci is a book written by Leonardo of Pisa, also known as Fibonacci, in 1202. It was one of the first Western books to introduce Hindu-Arabic numerals and the decimal number system to Europe, and it contains various mathematical topics, including puzzles and riddles.