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.
This size is common up until 1899. In 1899 a standard postcard size of 5.5 x 3.5 inches was introduced as the maximum size. The minimum size was 3.25 x 2.25 inches. The minimum size was raised to 4 x 2.75 inches in 1906 and in 1925 the maximum size was raised to 5.875 x 4.125 inches.