【正确答案】正确答案：When two sounds never occur in the same environment, they are in complementary distribution. For example, the aspirated English stops never occur after(s), and the unaspirated ones never occur initially. Allophones of the same phoneme are usually in complementary distribution. The allophones of/p/, for instance, are also in complementary distribution. The unaspirated(p =)occurs after /s/, while the aspirated(p ^h )occurs in all other environments except after /s/.