单项选择题 What the element ‘-es’ indicates is third person singular, present tense, the element ‘-ed’ past tense, and ‘-ing’ progressive aspect. Since they are the smallest unit of language and meaningful, they are also（）.

单项选择题 Of the three branches of phonetics, the longest established, and until recently the most highly developed, is（）phonetics.

单项选择题 In English, “pill” and “bill” are （）.