5．(2016·全国卷Ⅰ)The nursery team switches him every few ________ (day) with his sister so that while one is being bottle­fed, the other is with mum - she never suspects.

　　解析：days　every few days表示"每隔几天"，此处应该使用名词的复数形式days。

　　6．(2015·全国卷Ⅰ)I'd skipped nearby Guilin, a dream place for tourists seeking the limestone mountain tops and dark waters of the Li River which are pictured by artists in so many Chinese ________ (painting)．

　　解析：paintings　painting意为"图片，图画"，是可数名词，由于前有"so many"修饰，故使用其复数形式。

　　Ⅱ.单句改错

　　1．(2018·全国卷Ⅰ)Last winter when I went there again, they had a big separate house to raise dozens of chicken.

　　________________

　　解析：chicken→chickens　短语dozens of之后应该使用可数名词chicken"鸡"的复数形式。

　　2．(2018·全国卷Ⅱ)After supper, we would play card games of all sort in the sitting room.________________

　　解析：sort→sorts　由前面的all 修饰可数名词sort可知，应用sort的复数形式；all sorts意为"各种各样的"。

　　3．(2018·全国卷Ⅲ)At that moment, I remembered that my father once said, "The classroom is a place for learning and that includes learning from textbooks, and mistake as well."

　　________________

　　解析：mistake→mistakes　and连接两个平行成分，前面的textbooks为复数，故可数名词mistake"错误"应改为 mistakes。

　　4．(2017·全国卷Ⅰ)The instructor kept repeating the word, "Speed up！" "Slow down！" "Turn left！"________________

　　解析：word→words　根据后面引号内的内容可知教练一直重复说的话有多句，故此处应用word的复数形式。

5．(2016·全国卷Ⅲ)The teenage year from 13 to 19 were the most difficult time for