70's looks better than 70s (which is a serial number) and is an allegory for " the decade of the years between 1970 and 1979 (& 365/365.25's)".

Apostrophe - now when is the possessive not an implied and when is the abbreviation not a posessive and what about it's its. I never could figure the mnemonic for those two, too. There ain't no logic - it just is.

Now what are the plural of data? (or modem come to think of it)
and why is opera a collection of songs wot we call individually an opus? Plural of opera is.............

It(?)s anarchy out there and language lives or we call it LATIN.