单选题 The federal entity created by the Constitution is by far the dominant feature of the American governmental system. (1) the system itself is in reality a mosaic, (2) of thousands of smaller units--building blocks which together (3) the whole. There are 50 state governments (4) the government of the District of Columbia, and further down the ladder are still smaller units, (5) counties, cities, towns and villages. This (6) of governmental units is best understood (7) the evolution of the United States. The federal system, it has been seen, was the last step in the (8) process. Prior to its creation, there were the governments of the (9) colonies (later states) and prior to (10) , the governments of counties and smaller units. One of the first tasks (11) by the early English settlers was the creation of governmental units for the tiny (12) they established along the Atlantic coast. Even before the Pilgrims disembarked (13) their ship in 1620, they (14) the Mayflower Compact, the first written American constitution. And as the new nation pushed (15) each frontier outpost created its own government to manage its affairs. The drafters of the U. S. Constitution left this multilayered governmental system (16) . While they made the national structure supreme, they wisely (17) the need for a series of governments more directly in (18) with the people and more keenly attuned(合拍) to their needs. Thus, certain (19) such as defense, currency regulation and foreign relations--could only be managed by a strong centralized government. But (20) such as sanitation, education and local transportation--belong mainly to local jurisdictions(管辖权).