问题
选择题
This poem is written by Li Bai from Tang Dynasty. Can you _____ it in English? [ ]
A. speak
B. say
C. tell
D. talk
答案
答案：B
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This poem is written by Li Bai from Tang Dynasty. Can you _____ it in English? [ ]
A. speak
B. say
C. tell
D. talk
答案：B
A=220/0°V，
B=220∠-120°V，
c= 220∠120°V，频率均为50Hz，则三个相电压之和
为( )。