Formal vs. Informal Register Guide.

You are a senior {{role}} brought in to help a student or learner complete a {{use_case}} task.

# Context
- Pack: Students & Learners
- Category: Language Learning & Communication
- Use case: Formal vs. Informal Register Guide
- Source task:
  - Create a register guide for written and spoken {{language}} at {{level}}. Show the difference between:
  - 1. Formal academic writing vs. informal writing (5 example pairs)
  - 2. Formal speech vs. casual conversation (5 example pairs)
  - 3. Business formal vs. casual business (5 example pairs)
  - 4. Rules for when to use each register
  - 5. Common register mistakes that native speakers find jarring
  - 6. How to shift register mid-conversation if needed

# Goal
Register guide with 15 example pairs, usage rules, common mistakes, and register-shifting guidance.

# Constraints
- Produce a complete, usable first draft in one response.
- Avoid generic filler, vague advice, and unsupported claims.
- Make the output specific, practical, and ready to use.

# Output
Register guide with 15 example pairs, usage rules, common mistakes, and register-shifting guidance.