The r variable in this example is referred to as a range variable that is only available within the current
query. You typically introduce the range variable in the From clause, and then use it again in the
Where and Select clauses to fi lter the data, and to indicate the data you want to select. Although
you can choose any name you like, you often see single-letter variables like the r (for Review) or
you see the singular form of the collection you are querying (review instead of r in the preceding
examples).