66---70 CBBDC
66.C 点评：从第一段第二句话可知。
67.B 点评：第二段第三句话But as the number of children gets larger，conversation gives way to the parents’ efforts to control the loud noise they make.表明该题选B。
68.B 点评：在该句话后面，Lewis接着解释When you see someone get up from the table and walk around during dinner，chances are it’s the middle child，说明 the middle children不能得到太多重视。
69.D 点评：文章第三段第一句话 The study also provides an explanation for why middle children often seem to have a harder time in life than their siblings.表明答案为D。
70.C 点评：从第二段第4，5句话可以推知该题答案为C。