阅读下列材料，然后从A、B、C、D四个选项中选出能回答所提问题或完成所给句子的最佳选项。

One night, when I was eight, my mother gently asked me a question I would never forget. “Cindy, my company wants to promote (升职) me but needs me to work in Brazil. This is like your teacher telling you that you've done well and allowing you to skip (跳) a grade, but you'll have to leave your friends. Would you say yes to your teacher?” She gave me a hug and asked me to think about it. I was lost in thought. The question kept me wondering for the rest of the night. I had said “yes” but for the first time, I realized the difficult decisions adults had to make.

     For almost four years, my mother would call us from Brazil every day. Every evening I'd eagerly wait for the phone to ring and then tell her everything happened during the day. A phone call, however, could never take her place and it was difficult not to feel lonely at times.

During my fourth-grade Christmas break, we flew to Rio to visit her. Looking at her large empty apartment,   ▲  It was then I started to understand the difficult choices she had to make. She needed to think about both family and work. Faced with difficult decisions, she used to tell me, you wouldn't know whether you make the right choice, but you could always make the best out of the situation, with a positive attitude.

     Back home, I reminded myself that what my mother could do, I could, too. If she managed to live in Rio all by herself, I, too, could learn to be independent. I learn how to take care of myself and set high but achievable goals.

My mother is now back with us. But I will never forget what the experience has really taught me. I've learned a lot because of this separation. There are lots of difficult decisions that we have to face in our life. We need to have a positive attitude no matter what happens.

刘梦家中种了一些甜瓜，刘梦的爸爸经常会对甜瓜的植株进行“打杈”．刘梦爸爸如此做的原因是（　　）