For an opinion to be substantiated, you need supporting evidence or a reference to validate it. Option A qualifies as it mentions a verifiable fact by suggesting that one can check with the large computer company to see its origin. More evidence would be required to substantiate the claim that small businesses are the backbone of America's strong economy. Option C lacks easily accessible factual support, while D presents a more generalized statement.
The most appropriate choice is "A". One of the major computer companies started in a garage. Jeff Bezos initiated Amazon from his garage. Bill Gates and Paul Allen founded Microsoft, having limited resources in their small garage. Furthermore, the first film studio of Disney was located in the garage belonging to Walt Disney's uncle.
