Rather, all keywords in the Ad Group are looked at in an overview.
In other words, looking at all keywords taken together, the system decides what the Ad Group is about - and then places the ad (whether image or text) on a page of content about the same subject.
I made an ad that ONLY focus on "apple", but if google puts it in a "food" content site, it will be totally irrelevant.
Agreed. So it would very wise to make it clear in the keyword list that it is the computer and not the fruit that is being advertised.
AWA