(单选题)

According to the passage, what is the main reason for carmakers to make engines more efficient? ( )

A.Internal combustion engines are not efficient enough.

B.The tightened regulations on fuel and greenhouse gas emission.

C.In the future, cars will use electric engines.

D.The greenhouse gases and pollution start to make people sick.

参考答案：B

参考解析：

细节题。根据题干关键词car-makers和engines定位至首段Regulations on fuel economy and CO2 emissions are forcing car makers to make engines more efficient by 2025.可知迫使汽车制造商提高发动机效率的原因在于有关燃油经济性和碳排放的规定。选项A：内燃机效率不高；选项B：严格的燃油和温室气体排放规定；选项C：未来汽车将使用电发动机；选项D：温室气体和污染开始使人生病。观察选项可知只有选项B描述符合文意，故本题正确答案选B。

知识点：细节题英语阅读理解通用英语