Some scientists think that parents make too big fuss about hygiene, and that daily 【M1】 ______ contact with bacteria and viruses

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问题 Some scientists think that parents make too big fuss about hygiene, and that daily 【M1】 ______
contact with bacteria and viruses can be good for youngster. A recent study conducted 【M2】 ______
by the University Children’s Hospital in Munich showed that children who had
at least two mild virus infections before their first birthday were only the half as 【M3】 ______
likely to be diagnosed with asthma or allergies when they were seven, compare with 【M4】 ______
children who had been ill only once or not at all. This finding supports the hypothesis 【M5】 ______
that today’s ultra-clean lifestyle is the reason of an increase in allergies in the general 【M6】 ______
population in developed countries. It is possible, although this is not yet establish, 【M7】 ______
which contact with the bacteria is needed for cells in human immune systems to 【M8】 ______
develop correct. So parents should not overreact if their children get muddy or 【M9】 ______
dirt sometimes when playing outside. 【M10】______
【M7】

选项

答案establish→established

解析 (establish为及物动词,it与establish是被动关系,故用过去分词形式。)
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