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.
The alcohol percentage in vodka ranges. Vodka usually has an alcohol content of 35% to 50% by volume. The classic Polish, Lithuanian and Russian vodka is 40% (80 proof).