Two system of weights and measures exist in the U. S. today: the U. S. Customary System an

d the International System of Units (IS, after the initials of International System). IS, commonly referred to as the metric system, is actually a more complete, coherent version of it. Throughout U. S. history, the Customary System (inherited from, but now different from, the British Imperial System) has been customarily used; a plethora of federal and state legislation has given it, through implication, standing as the primary weights and measures system. The metric system, however, is the only system that Congress bus ever specifically sanctioned. An 1866 law reads:

It shall be lawful throughout the United States of America to employ the weights and measures of the metric system; and no contract or dealing or pleading on any court, shall be deemed invalid or liable to objection because the weights or measures expressed or referred to therein are weights or measures of the metric system.

Since that time, use of the metric system in the U. S. has slowly and steadily increased, particularly in the scientific community, in the pharmaceutical industry, and in the manufacturing sectorthe metric system is now predominantly used.

On Feb. 10, 1964, the National Bureau of Standards (now known as the National Institute of Standards and Technology) issued the following bulletin:

Henceforce it shall be the policy of the National Bureau of Standards to use the units of the International system (iS), as adopted by the 11th General Confference on Weights and Measures (October 1960), except when the use of these units would obviously impair communicator or reduce the usefulness of a report.

On Dec. 23, 1975, Pres. Gerald R. Ford signed the Metric Conversion Act of 1975. It defines the metric system as being the International System of Units as interpreted in the U. S. by the secretary of commerce.

The Trade Act of 1988 and other legislation declare the metric system the preferred system of weights and measures for U. S. trade and commerce, call for the federal government to adopt metric specifications, and mandate the Commerce Dept. to oversee the program, the conversion process is currently underway: however, the metric system has not become the system of choice for most American daily use.

The following seven units serve as the base for the International System: length-meter; masskilogram; time second; electric current-ampere; thermodynamic temperature-kelvin; amount of substance-mole; and luminous intensity-candela

Two systems of weights and measures used in the U.S. are ______.

A．the U. S. Customary System and the metric system

B．the International System and the metric system

C．the Imperial System and the metric system

D．the Customary System and the Imperial system