当直径为100mm以下的煤气管道着火时可以（）止火。

A.用灭火器

B.用遮挡灭火

C.关阀门

D.人工浇水

纤维不存在（）

A．Bundles of partially lignified fibres with crystal sheaths

B．Numerous colourless single fibres, often whole with narrow lumen

C．Parenchymatous cells，fibres，and vessels

D．Starch granules present，fibres and sclereids absent

E．Fibres with crystal sheath containing calcium oxalate prisms