All the children on the playground stared up into the sky until the noise of the plane _____.[ ]

A. died away                            

B. died out  

C. gave away                        

D. gave out

某N600机组的速度变动率δ＝5%，并网运行时同步器工作范围为＋4%～－6%。问：（1）在电网频率为50Hz时，机组最多能带多少负荷？（2）当电网频率在何值时，机组才能带满负荷？