下列灭火剂能用于扑灭金属钠着火的是（ ）
A．煤油
B．砂土
C．干粉（含NaHCO3）灭火剂
D．水
答案：B
― It' a fine day. Shall we go jogging?
― ______ But we need to be home before six.
A．Have a nice time!
B．Not at all.
C．You are right.
D．Good idea!
A．变压器输出端所接电压表的示数为20V
B．变压器的输出功率为200W
C．变压器输出端的交流电的频率为50Hz
D．穿过变压器铁芯的磁通量变化率的最大值为20/n2Wb/s
V
/n2Wb/s