问答题 America"s population hit the 300 million mark yesterday—at 7:46 a.m. Eastern time, according to Census Bureau estimates. Nobody knows exactly who became America"s 300 millionth citizen. But demographers are summing up the milestone as a turning point that signals several trends to watch as the U.S.—in contrast with Europe and Japan—deals with a steadily growing population.
Politically and demographically, experts say, the shifts will begin to have an impact on regions of the country not yet used to the new diversity provided by the influx of Hispanics and Asians, which has already transformed California, Arizona, Texas, Florida, and New York.
In coming years, Midwesterners, those in the Great Plains, rural areas, and small towns everywhere will begin to deal with the challenges of new ethnic and racial residents, says William Frey, a population expert at the Brookings Institution in Washington. And the country as a whole will begin to be more dominated by a young/ old divide than the current liberal/conservative model that dominates political discourse.
"This means we are going to transform the current, red/blue political dichotomy to one where the nation is separated by age ... young vs. old," says Mr. Frey. "The issues of younger generations dealing with children and opportunities for minorities will clash with those of the aging baby boomers whose voters are concerned with issues of aging and Social Security and Medicare," he adds. "Both parties will have to adjust to this new dichotomy."
The new milestone hasn"t generated much hoopla. That"s in sharp contrast to 1967, when President Johnson hailed the 200 millionth American, and Life magazine dispatched a cadre of photographers to find a baby born at the exact moment. One reason is that population growth has become controversial, especially in an election year when immigration is a hot-button issue and politicians are wary.
Commerce Secretary Carlos Gutierrez says the Bush administration is not playing down the milestone, though he had no plans for Tuesday. "I would hate to think that we are going to be low-key about this," he says, since growth helps the economy.
While it"s hard to prove that population growth spurs economic growth, the two often go hand in hand, according to experts quoted in the Monitor"s recently published series: "U.S. population: 300 million. " For example: a nation with a rising population can support its retirees far more easily than one with a declining population. That"s an advantage for the U.S., which is virtually the only developed nation expected to grow this century.
But population growth has less rosy implications, the Monitor series points out. Some experts worry that the land can"t sustain the extra 100 million people expected by 2043. Another challenge is sprawl, the dominant model of development, which gobbles up forest and prairie.

问答题 Why does the author say that the nation"s reaction to the new milestone of 300 million is "in sharp contrast to 1967" (para. 5)?

问答题 Introduce briefly population expert William Frey"s comment on the challenges from the growth of America"s population.

问答题 Why does the Monitor say that "population growth has less rosy implications" (para. 8)?