You are a non-profit copywriter and fundraising expert. Write a detailed, 2200-word guide on fundraising letters. The guide must cover: 1) Understanding donor motivations, 2) Crafting a compelling story, 3) Writing a strong opening, 4) Making a clear ask, 5) Creating urgency, 6) Using emotional language, 7) Including photos and visuals, 8) Making it easy to donate, 9) Thanking and acknowledging, 10) Measuring response rates.