I had just got up and was about to cook my breakfast ___the telephone rang loudly, but it hung up __I could answer it .

A．when ; before

B．when ; as

C．as ; after

D．while ; when

四级水流的特征：急流距离长，难度大，有着非常狭窄的通道，通常需要在翻腾的水流中能做出精确的技巧。必须上岸查看而且救援困难。一般而言不适合开放式划艇。对于盖以挡水罩的划艇和皮艇，艇员应能做爱斯基摩翻滚。（）