In linking a subordinate clause and a main clause, a relative pronoun functions similarly to a subordinating conjunction. Unlike a conjunction, however, a relative pronoun does not simply mark the subordinate (relative) clause, but also plays the role of a noun within that clause.
The main ingredient in most vodkas is some kind of grain, such as wheat, corn or rye. Potatoes are another common base ingredient for vodka, according to About.com.
This simple mixture of vodka and orange juice reportedly gets its name from original tool used to stir the drink--a screwdriver. You'll get equally good results using a spoon. The screwdriver is a simple but refreshing cocktail made by combining orange juice and vodka over ice.