Information: - Hydrogen is a chemical element with chemical symbolH and atomic number1. With an atomic weight of , hydrogen is the lightest element on the periodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass. Non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed "protium" (name rarely used, symbol H), has one proton and no neutrons. - Helium is a chemical element with symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas, the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements. - The American Blimp A- 170 is a blimp built by the American Blimp Corporation now owned and operated by the Van Wagner Airship Group . - A rigid airship is a type of airship (or dirigible) in which the envelope is supported by an internal framework rather than by being kept in shape by the pressure of the lifting gas within the envelope, as in blimps (also called pressure airships) and semi-rigid airships. Rigid airships are often commonly called Zeppelins. - A Zeppelin was a type of rigid airship named after the German Count Ferdinand von Zeppelin who pioneered rigid airship development at the beginning of the 20th century. Zeppelin's notions were first formulated in 1874 and developed in detail in 1893. They were patented in Germany in 1895 and in the United States in 1899. After the outstanding success of the Zeppelin design, the word "zeppelin" came to be commonly used to refer to all rigid airships. Zeppelins were first flown commercially in 1910 by Deutsche Luftschiffahrts-AG (DELAG), the world's first airline in revenue service. By mid-1914, DELAG had carried over 10,000 fare-paying passengers on over 1,500 flights. During World War I the German military made extensive use of Zeppelins as bombers and scouts, killing over 500 people in bombing raids in Britain. - Because of Archimedes' principle, a lifting gas is required for aerostats to create buoyancy. Its density is lower than that of air (about 1.29kg/m, 1.29 g/L). Only certain lighter than air gases are suitable as lifting gases. - A blimp, or non-rigid airship, is an airship (dirigible) without an internal structural framework or a keel. Unlike semi-rigid and rigid airships (e.g. Zeppelins), blimps rely on the pressure of the lifting gas (usually helium, rather than hydrogen) inside the envelope and the strength of the envelope itself to maintain its shape. The term is sometimes also used to refer to the tethered craft properly known as moored balloons. While often very similar in shape, moored balloons have no propulsion and are tethered to the ground. - An airship or dirigible balloon is a type of aerostat or lighter-than-air aircraft that can navigate through the air under its own power. Aerostats gain their lift from large gas bags filled with a lifting gas that is less dense than the surrounding air. In early dirigibles, the lifting gas used was hydrogen, due to its high lifting capacity and ready availability. Helium gas has almost the same lifting capacity and is not flammable, unlike hydrogen, but is rare and relatively expensive. Significant amounts were first discovered in the United States and for a while helium was only used for airships by the United States. Most airships built since the 1960s have used helium, though some have used hot air. Given the information above, choose from the list below the object entity that exhibits the relation 'subclass of' with the subject 'american blimp a-170'. Choices: - aircraft - airship - balloon - blimp - bombing - chemical element - chemical substance - craft - density - envelope - germany - helium - hydrogen - isotope - lighter - mass - name - noble gas - number - own - paying - people - point - principle - propulsion - proton - rigid airship - service - shape - table - type - word - zeppelin
A:
aircraft