Complex sentence: At the start of the book, it is spring time, the weather is fine, and good-natured Mole loses patience with his spring cleaning and flees his underground home, heading up to take in the air.
Split into simpler sentences: At the start of the book, it is spring time: the weather is fine, and good-natured Mole loses patience with spring cleaning. He flees his underground home, heading up to take in the air.