I _________ my mum cook dinner in the kitchen when the telephone ______.

A．helped; was ringring

B．helped; rang

C．was helping; rang

D．was helping; was ringing

经测试，高于（）的噪声会使人心情烦躁、疲倦，工作效率下降等，甚至引发头晕、失眠等病症。