input: Write a function to simulate a quiz game where questions are chosen randomly from a list, and the player has 30 seconds to answer as many as possible.
  assert isinstance(start_game(), int)
  assert len(questions) > 0
  assert isinstance(questions[0], dict)
output: import random
  import time
  
  questions = [
      {"question": "What is the capital of France?", "answer": "Paris"},
      {"question": "What is 2 + 2?", "answer": "4"},
      {"question": "What is the color of the sky on a clear day?", "answer": "Blue"},
      {"question": "Who wrote 'To Kill a Mockingbird'?", "answer": "Harper Lee"}
  ]
  
  def start_game():
      score = 0
      start_time = time.time()
      while time.time() - start_time < 30:
          question = random.choice(questions)
          print(question["question"])
          user_answer = input("Your answer: ")
          if user_answer.lower() == question["answer"].lower():
              score += 1
      return score