What is an appropriate response to someone saying "merci" in French?

Read also:

• Physicists Propose Cheaper Alternative to Particle Colliders: Supermassive Black Holes - Gizmodo
• Who is your favorite young adult author and what is your favorite book by them? What makes it stand out from their other works?
• Why are there no fossils for the 'missing link' that connects our ancestors with other species? Is this a misconception or is there another explanation?
• Eric Mangini defends Shedeur Sanders after speeding incidents - New York Post
• Scientists stunned to see humpback whales trying to send messages to humans - BBC Wildlife Magazine
• Does whey protein affect the kidneys?
• Quantum embezzlement is hiding in known one-dimensional materials: Study - Interesting Engineering
• What is the reason for writing X^2 as XX instead of X*X?
• How do introverts celebrate their birthday?
• Were the 1980s as uptight and prudish as movies and TV shows make them out to be? When I think of 80s culture, I think about a very "icky" judgmental yuppie status quo time period.
• Eating More of These Foods May Lower Your Cancer Risk by 8%, New Study Suggests - EatingWell
• Jack Betts, ‘Spider-Man’ Actor and Spaghetti Western Veteran, Dies at 96 - Variety
• Carrying own bag after splitting with caddie, Max Homa fails to qualify for U.S. Open - NBC Sports