When I was in high school back in the 1970s, I was taught that to make a plural of an acronym, a letter, or a number, one should add an apostrophe and "s". Like I would have written this sentence, ...
Possible Duplicate: What is the correct way to pluralize an acronym? Let's say we're talking about PLCs (programmable logic controllers)? Or are they "PLC's"? I've seen it both ways!
I was reading this documentation file of some software and note the plural spelling of this abbreviation is “URL’s”. Why isn’t it “URLs”?