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Once you have decided whether to write in the present tense or the past
tense, you must remain consistent. You cannot shift tenses in the middle of a
sentence or the middle of a paragraph unless there is a reason within the
context of the writing to make a change in time. In other words, you can't go
from the past to the present and back to the past if all the events you are
describing occurred in the past. You must remember when you are editing to check
the tenses to be sure that you have been consistent with the choices you've
made. Correcting shifts is easy. Simply choose one of the tenses and make
everything with in the sentence that tense.

Voice describes the subject of the sentence. When the subject of the sentence
does the action of the sentence, it is considered active. When the subject of
the sentence does not do the action with in the sentence, the subject is
considered passive. Passive voice is wordier and weaker than active voice so you
should avoid using it whenever possible