【正确答案】 C

【答案解析】第二段里“…，but failed to establish a link with radiation or pollution”这句话证明A是错的；“You would get an increased risk of it if you suddenly put a lot of people from large towns in a rural area,…”则证明B是错的，“Childhood leukaemia appears to be an unusual result of a common infection”证明D是错的；“Our study shows that population mixing can account for the leukaemia cluster and that all children，...”证明C是正确的。所以此题正确答案应当为C。