题目内容：
根据材料，回答问题。Directions: In this section, you will hear 3 short passages. At the end of each passage, you will hear some questions. Both the passage and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices markedA．,B．, C． and D．. Then mark the corresponding letter on Answer Sheet I with a single line through the centre.
Passage One
Questions 16 to 18 are based on the passage you have just heard.
A．Electric cars.
B．Increasing fuel efficiency.
C．California's pollution laws.
D．Automobile safety.
参考答案：
答案解析：