Read the following passage and answer the questions given after it.
Passage:

We are all born milk drinkers. Babies’ guts produce the enzyme lactase, which breaks down lactose, the sugar in cow’s milk, into the simpler sugars —- glucose and galactose. But for the majority of humans, production of the enzyme lactase plummets after weaning. “From a human perspective — no, to go further than that, from a mammalian perspective — the norm is to be able to tolerate your mother’s breast milk, and then as you get past infancy, to stop producing lactase and become lactose intolerant,” said Adam Fox, a consultant paediatric allergist at Guy’s and St Thomas’s hospitals, and one of the UK’s leading food allergy experts. “Then you’ve got a small group of humans that have a mutation which means they maintain production of lactase into adulthood. Northern Europeans, the Masai [in east Africa], some Arab groups as well. But that’s the exception, not the rule.”

That schism between milk-drinkers and the rest — actually a series of independent genetic mutations — appears to have occurred about 10,000 years ago, around the time humans were domesticating farm animals. It is the reason that in countries such as the UK, Sweden and Ireland, more than 90% of adults can drink milk without suffering any ill effects, but worldwide, more than two-thirds of all adults are considered lactose intolerant. For lactose-intolerant people, a glass of milk can induce bloating, stomach pains and diarrhoea. (Lactose intolerance should not be — though often is — confused with cow’s milk allergy, an immune response to the proteins in cow’s milk that affects around 1% of UK adults.)

Even in northern Europe, milk as we know it is a recent phenomenon. Fresh milk, left unrefrigerated, spoils quickly and can harbor a variety of deadly pathogens, including E Coli and tuberculosis. For most of history milk was either consumed within moments of milking or
processed as cheese or yoghurt. Few drank milk in its liquid form. “The Romans considered it a sign of barbarism,” said Mark Kurlansky, author of Milk! A 10, 000—Year FoodE'acas. “The only people who drank milk were people on farms, because they were the only ones who could get it fresh enough.” Even then, cow’s milk was considered inferior to alternatives such as goat or donkey. In the 19th century, “swill milk” — so called because cows were fed the filthy runoff from inner-city breweries, turning their milk blue — was linked with thousands of infant deaths. Only in the early 20th century, with the introduction of mandatory pasteurization — in which milk is heated to kill off any bacteria before bottling — did milk become safe enough for most people to drink regularly.)