[单项选择]What is happiness Most researchers agree that it involves an assessment of the good and bad in our lives. It"s the emotional balance sheet we keep that allows us to say honestly whether we"re living a happy life, in spite of bad things now and then.. Marriage has taken a lot of hits since the 1960s. It"s been said to hold many people, especially women, back from their full potential to be happy. Don"t believe it. In 2004, 42 percent of married Americans said they were very happy. Just 23 percent of never-married people said this. The happiness numbers were even lower for other groups: Only 20 percent of those who were widowed(死了丈夫或妻子的), 17 percent of those who were divorced, and 11 percent of those who were separated but not divorced said they were happy. Overall, married people were six times more likely to say that they were very happy than to report that they were not too happy. And generally speaking, married women say they"re happy more often than married men. Marriage isn"t just associated with happiness -- it brings happiness, at least for a lot of us. One 2003 study that followed 24,000 people for more than a decade documented a significant increase in happiness after people married. For some, the happiness increase wore off in a few years, and they ended up back at their premarriage happiness levels. But for others, it lasted as long as a lifetime.What is the conclusion of the 2003 study about happiness
A. Marriage brought happiness to all the married people.
B. Happiness levels usually dropped in a few years after marriage
C. Most people remained at their premarriage happiness levels.
D. Happiness greatly increased for many married people.