PHP, Composer, and a Modern Dev Environment

What's the relationship between composer.json and composer.lock?

• AThey are identical, one is just renamed
• Bcomposer.json declares constraints (your intent: 'Guzzle ^7.5'); composer.lock records the exact versions Composer resolved at install time, so other people get the same versions
• Ccomposer.lock is generated by composer.json on demand and shouldn't be committed
• Dcomposer.json is for development, composer.lock is for production