动词不定式作主语和表语 — 英语选择题

下列句子中，动词不定式（短语）作表语的一项是（　　） A. To give up smoking is the first step towards a healthier lifestyle. B. It took him a whole year to get rid of his junk food habit. C. The best way to stay healthy is to balance work and rest. D. It is necessary for teenagers to limit their screen time every day.