I------------the grocer for 20 years. ?

The correct choice for the sentence “I------------the grocer for 20 years.” is C) “have known.” This option is in the present perfect tense, which is used to indicate an action that started in the past and continues to the present or has relevance to the current moment.

In this context, "have known" signifies that the speaker's acquaintance with the grocer began 20 years ago and is still ongoing. The present perfect tense effectively captures the duration of the relationship indicating not just the fact that they know the grocer, but also the length of time that this knowledge has persisted.

In contrast, other options are either grammatically incorrect or do not fit the context. Option A) “know” is simple present tense, which implies a general truth but does not convey the sense of duration. Option B) “am know” is ungrammatical as "know" cannot follow the verb "to be" in this context. Option D) “have been knowing” is grammatically correct but not commonly used since "know" is a stative verb that typically does not use continuous forms. Therefore, “have known” is the most appropriate and grammatically sound choice.