单选题

A Immigrants to the USA often keep their own ethnic characteristics.

B Immigrants to the USA contribute a lot to their adopted land.

C Stew has a distinctive flavour.

D Americans of German ancestry have made a great contribution to the USA.

解析：
[考点]主旨题。录音开始就用“pot of stew”形象地形容了美国内部各族群之间的关系，即各自保留自己的特色，之后就是详述这种现象。可知，文章的主旨是A项，即美国的移民通常都会保留自己的特色。