根据下面资料，回答
A proverb from ancient China was widely spread in the West: "If you want to be happy for a few hours, go to get drunk; if you want the happiness to last three years, get married; if you want lifetime happiness, take up gardening." The reason for the last is this: Gardening is not only useful, but it helps you to identify yourself with nature, and thus brings you new joy each day besides improving your health.
A research of a US university that I′ve read gives a definition of happiness as what makes a person feel comfortably pleased. To put it simply, happiness is an active state of mind where one thinks one′ s life is meaningful, satisfactory and comfortable. This should be something lasting rather than transitory.
Lots of people regard it the happiest to be at leisure. But according to a study, it is not a person with plenty of leisure but one at work that feels happy, especially those busy with work having little time for leisure. Happiness does not mean gains one is after but a desire to harvest what one is seeking for. People often do not treasure what they already have but desire what they cannot get. That is somewhat like a man with fond dreams of numerous lovers while unwilling to settle down with the woman beside him.
Happiness is a game balancing between two ends--what one has and what one wishes for, i.e. one′s dream and the possibility to realize it. The study comes to this conclusion: A happy man is one who aims high but never forgets his actual situation; one who meets challenges that develop his ability and potentiality; one who′s proud of his achievements and the recognition given to him. He has self-respect and self-confidence; treasures his own identity and loves freedom. He is sociable and enjoys wide range communication with others; he′s helpful and ready to accept assistance. He knows he is able to bear sufferings and failures; he is sensible enough to get fun from daily work. He is a man capable of love and passion.
The research of the US university found that most people feel happy when they_____________.

A.are after their goals
B.work as gardeners
C.are at leisure
D.have great leisure