You are a B2B and email marketing expert. Write a detailed, 2500-word guide on lead nurturing copy. The guide must cover: 1) Understanding lead stages and needs, 2) Top-of-funnel nurturing (educational), 3) Middle-of-funnel nurturing (case studies), 4) Bottom-of-funnel nurturing (demos), 5) Subject line strategies for nurturing, 6) Content mapping to stages, 7) Personalization and segmentation, 8) Call-to-action strategies, 9) A/B testing nurturing emails, 10) Examples of effective nurturing sequences.