Table of contents
First and second reference
The first time a single countable noun is introduced, use a. Thereafter, when referring to that same item, use the.
Example
Television is now commonplace, but few people understand how it works. Inside the television, a tiny camera breaks down pictures and sends them to a transmitter. Once the transmitter has received the pictures, it transmits them to a receiver...
Fill in the blanks with a / an, the, or x (no article). Think about whether the noun is being referred to in a general, non-specific or specific way. Then check your answers by clicking on the button 
next to each box.
Making distilled water
distilling flask is attached to condenser, as shown in the diagram. condenser is connected to source of cold water and beaker is placed below it. flask is partially filled with water. thermometer is inserted through the stopper ( stopper seals flask). flask is heated with Bunsen burner. When water boils, it becomes steam. steam rises in flask and passes through condenser, where it is cooled. condensed steam collected in beaker is distilled water.
(from Master, PA, (1986) Science, Medicine and Technology: English grammar and technical writing, Prentice-Hall Regents, New Jersey.)
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