用示波器观察1Hz的正弦波,时基取多少,可清晰观察两个周期的完整波形(屏幕分十格)
A. 200ms
B. 100ms
C. 50ms
D. 20ms
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The Grand Canyon in north-western ___ ____ is one of nature's most impeessive sights.
A. Utah
B. Arizona
C. Nevada
D. Idaho
The United States went to war with ___ ____ in 1812, the last war fought between these two countries.
A. Britain
B. France
C. Spain
D. Mexico
In 1932, in the depth of the depression, the American people chose ___ ____ as their next president who promised a "new deal" to get America out of depression.
A. Theodore
B. Franklin Roosevelt
C. Woodrow Wilson
D. Herbert Hoover