题目内容：
共用题干Dangers Await Babies with Altitude
Women who live in the world's highest communities tend to give birth to under-weight ha-bies,a new study suggests.These babies may grow into adults with a high risk of heart disease and strokes.
Research has hinted that newborns in mountain communities are lighter than average.But it wasn't clear whether this is due to reduced oxygen levels at high altitude or because their mothers are under-nourished—many people who live at high altitudes are relatively poor compared with those living lower down.
To find out more,Dino Giussani and his team at Cambridge University studied the records of
400 births in Bolivia during 1976 and 1998.The babies were born in both rich and poor areas of two cities:La Paz and Santa Cruz. La Paz is the highest city in the world,at 3 .65 kilometers a-bove sea level,while Santa Cruz is much lower,at 0.44 kilometers.
Sure enough,Giussani found that the average birthweight of babies in La Paz was significant-ly lower than in Santa Cruz.This was true in both high and low-income families.Even babies born to poor families in Santa Cruz were heavier on average than babies born to wealthy families in lofty La Paz.“We were very surprised by this result,”says Giussani.
The results suggest that babies born at high altitude are deprived of oxygen before birth.
“This may trigger the release or suppression of hormones that regulate growth of the unborn child,”says Giussani.
His team also found that high-altitude babies tended to have relatively larger heads compared with their bodies. This is probably because a fetus starved of oxygen will send oxygenated blood to the brain in preference to rest of the body.
Giussani wants to find out if such babies have a higher risk of disease in later life.People born in La Paz might be prone to heart trouble in adulthood,for example.Low birth weight is a risk factor for coronary（冠状的）heart disease. And newborns with a high ratio of head size to body weight are often predisposed to high blood pressure and strokes in later life.
Giussani and his team are sure that______.
A: babies born in La Paz are on average lighter than in Santa Cruz
B: people living in La Paz are poorer than those in Santa Cruz
C: the birth weight of babies born to wealthy families is above average
D: mothers in La Paz are commonly under-nourished
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