阅读理解   Will fatherhood make me happy? That is a question many men have found themselves asking, and the scientific evidence is equivocal. A lot of studies have linked parenthood—particularly fatherhood—with lower levels of marital satisfaction and higher rates of depression than are found among non-parents.
    To investigate the matter further, psychologist Sonja Lyubomirsky decided both to study the existing literature, and to conduct some experiments of her own. The results suggest parenthood in general, and fatherhood in particular, really are blessings, even though the parent in question might sometimes feel they are in disguise.
    Dr. Lyubomirsky's first port of call was the World Values Survey. This is a project which gathers huge amounts of data about the lives of people all around the planet. For the purposes of her research, Dr. Lyubomirsky looked at the answers 6,906 Americans had given, in four different years, to four particular questions. These were: how many children the responder had; how satisfied he (or she) was with life; how happy he was; and how often he thought about the meaning and purpose of life.
    She found that parents had higher happiness, satisfaction and meaning-of-life scores than non-parents. The differences were not huge, but they were statistically significant. Moreover, a closer look showed that the differences in happiness and satisfaction were the result of men's scores alone going up with parenthood. Those of women did not change.
    Armed with this result, Dr. Lyubomirsky conducted her own experiment. The problem with projects like the World Values Survey is that, because participants are asked to recall their feelings rather than stating what they are experiencing in the here and now, this might lead them into thinking more fondly in hindsight about their parenting duties. Dr. Lyubomirsky therefore gave pagers to 329 North American volunteers aged between 18 and 94, having first recorded, among other things, their sex, age, ethnicity, socioeconomic status, marital status and number of children. She told them they would be paged at random, five times a day. When they were so paged, they were asked to complete a brief response sheet about how they felt, then and there. She did not, however, tell them why she was asking these questions.
    The upshot was the same as her findings from the World Values Survey. Parents claimed more positive emotions and more meaning in their lives than non-parents, and a closer look revealed that it was lathers who most enjoyed these benefits.
    It looks, then, as if evolution has bolted into men a psychological mechanism to keep them in the family. At first sight, it is strange that women do not share this mechanism, but perhaps they do not need to. They know, after all, that the children are theirs, and that a man's potential to father an indefinite number of offspring if he can find willing volunteers, might encourage him to stray from the bosom of his family. Enjoying fatherhood, by contrast, will help keep him in the porch.

单选题     The word 'equivocal' (Line 2, Para. 1) most probably means ______.

单选题     It can be inferred from the second paragraph that ______.

单选题     According to the passage, the World Values Survey ______.

单选题     In her experiment, Dr. Lyubomirsky laid emphasis on ______.

单选题     Which of the following can be seen as Dr. Lyubomirsky's result from her project? ______