Subjects tell the listener and the reader whom or what the sentence is about. The subject is that part of a sentence which names a person, thing, or idea. e.g. Every complete subject contains a simple subject. The simple subject, which is a noun or pronoun, is the most important word in the complete subject.
The USPS considers a postcard to be any single rectangular piece of paper that is at least 3 1/2 inches high by 5 inches long by 0.007 inch thick' and no more than 4-1/4 inches high by 6 inches long by 0.016 inches thick.. The post office considers all papers outside of these dimensions to be letters.
These specifications have been put in place to help make address reading easier. In the United States, first class mail necessities envelopes of the letter size. The dimensions must be between 5 inches and 11.5 inches wide, 3.5 to 6.125 inches high, and 0.007 to 0.25 inches thick. Post office preferred envelopes in Australia have 4 boxes with orange colored inks at the right hand part.