In some cases , yes.
You use he or she when you already have referred to a person in a sentence before, or earlier in the same sentence.
Because Viagra is it produced earlier then Levitra or Cialis
There is no past tense for the word left. You can use already left for it.
no you can't
earlier, formerly, previously, before now
The synonyms are earlier, formerly, previously, hitherto, or already.
The answer for A+ would be all of them
No. Baths already existed in earlier ancient civilisations.
Cars don't use generators because the batery is already generating energy. They use alternators in order to convert the energy generated into a usable form.
Earlier plants required water for reproduction. Gymnosperms can just use wind instead to reach an ovule where it will germinate.
Precedent:)
What else can you do to occupy yourself instead of asking these stupid questions on Wiki Answers? =)