Who does the author believe is responsible for changing his attitude?

Choices:
A. not enough information
B. himself
C. Kurt
D. his wife
himself
Kurt Vonnegut, writer and famous speech giver at US university graduation ceremonies, made this point to one group of soon-to-be-non-students: If this isn't nice, I don't know what is.
It is the end of a story about his grandpa who, on a summer's afternoon, would find the shade of a tree under which he could rest with a glass of homemade lemonade. The family didn't have a lot of cash, the grandpa worked hard every day of his life, but no matter how relentless the day-to-day was, he would always repeat this phrase as a reminder to those around him that, at the end of the day, this is all still amazing to be part of.
This kind of optimism, as you might call it, can often disappear in a flash in the busy-ness of business or school. Things become impossible, hardgoing, relentless(ly difficult). And the reasons we give for that busyness nearly always involve someone or something else - the system, the job, the weather...
For many years, people would ask the salutary "how are you?" and my answer was a stock one: "I'm tired."
It was my wife who pointed it out to me, presumably because everyone else was too polite to express their boredom with my reply. The fact is, most people feel tired most of the time, until they make a switch in their life. That switch is deciding that the only person who can turn that frown upside down, who can make crazy stuff happen (or attempt to, and enjoy the process), is you. And in Vonnegut's case, that switch came from saying out loud the one phrase that brings us back to the good elements in what we or our team or our family is doing at any given moment: If this isn't nice, I don't know what is.