Years can be measured in hundreds; a hundred years is a century.
Hundreds of millions of years
hundreds
people hundreds years ago used pencil and paper to measure
years or year's
No
No, the correct phrasing would be "It has been 5 years since I have known him."
No that isn't grammatically correct. You should say 'Though George didn't like the school, he studied in the same school for ten years'
No, the correct phrasing should be "for the last 10 years" to indicate a period of time that has lasted up to the present moment.
It has been 5 years since you knew him.Read more: It_has_been_5_years_since_you_knew_him._Is_this_sentence_grammatically_correct
The correct spelling of the plural noun is centuries (hundreds of years).
The correct way is to write New Year's Eve.
Yes, this is correct.
No. It is a sentence fragment.
20-year warranty would be correct: 20-year is a compound adjective applied to warranty.
Years can be measured in hundreds; a hundred years is a century.
If you use the "had" it implies that you no longer know this person. I had known means I don't know now. I have known means that you may or may not know her now.