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.
Vodka martini. A vodka martini, also known as a vodkatini or kangaroo cocktail, is a cocktail made with vodka and vermouth, a variation of a martini. A vodka martini is made by combining vodka, dry vermouth and ice in a cocktail shaker or mixing glass. The ingredients are chilled, either by stirring or shaking, then strained and served  straight up  (without ice) in a chilled cocktail glass.