By using what John Lennon said, the writer intends to ______.

参考解析：

推理判断题。根据该句前后的内容“Unfortunately, the same mental dynamics that tells us to look toward the future will only repeat themselves so that ‘someday’ never actually arrives.”和“When we are busy making other plans, our children are busy growing up, the people we love are moving away and dying, our bodies are getting out of shape, and our dreams are slipping away. In short, we miss our life.”可知，我们所期待的未来可能永远不会来，当我们在为未来做计划时，可能所有都会发生改变，由此可推测，作者引用John Lennon的话是为了建议人们把注意力集中在现在的生活上。故选A。