输油管道室外管线应每隔100m设一处接地,室内管线每隔30m设一处接地。( )
参考答案:对
I can __ my room. [ ]
A. clean
B. cleaning
C. cleaned
种子萌发时最先突破种皮的是( )
A.胚芽
B.胚轴
C.胚根
D.子叶