Why do nearly all English Bible translations ADD an "a" before the anarthrous pre-verbal predicates here:?

John 4:19
John 6:70
John 8:44 (twice)
John 9:17
John 10:1
John 10:13
John 10:33
John 12:6

There is no "a" in the Greek text before these pre-verbal predicate nouns.

Yet in each instance, an "a" is ADDED in translation.
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