Did you teach them how____(sing) that English song?

it...to learn an

选B.分析：因为english发原音,所以排除a.再看C,the是对某物的特指,
1.指上文提到过的人或物
2.谈话双方都知道的人或物
3.特指的人或物
e.g.The man who wrote this book is famous.
4.独一无二的事物
e.g.the sun,the moon,the earth
5.最高级和序数词前
e.g.the highest building,the first floor
6.用于形容词前指一类人或物
e.g.the old,the rich
7.地理名称、海洋名称前
e.g.the Sahara,the Atlantic
8.年代前
e.g.She grew up in the seventies.
9.西洋乐器前
e.g.play the piano,play the violin
10.姓氏复数前指一家人
e.g.the Smiths,the Greens
11.方位名词前
e.g.on the left,the south
12.专有名词前
e.g.the US,the Chinese Communist
13.the only,the very,the same…
以上情况用the.D（不说了,肯定不选.）