According to the passage, which of the following statements is true？
A. Scientists have managed to know more things about asteroid 1950 DA.
B. Many people seem to be worried about the predicted asteroid smash.
C. Scientists are still quite optimistic about man"s future.
D. The Earth is faced with frequent threats from space.
【C1】
A. taken
B. pieced
C. kept
D. made
某正弦交流电压为u＝311sin(100πt-π/3)V，它的电压有效值为()V。
A. 311
B. 100
C. 220
D. 380
近期采用的治疗中，哪项是错误的
A. 地高辛
B受体阻滞剂
C. 利尿剂
D. ACEI
E. ARB
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