人工燃气中一氧化碳的含量应小于（）％

A.0.02%

B.0.2%

C.2%

D.20%

A.10－20%

B.30－50%

C.23－30%

A.30ppm

B.50ppm

C.24ppm

D.20ppm

A.＜1ppm

B.＜2ppm

C.＜5ppm

D.＜9ppm

A.15至 20

B.30

C.60

A.15 ％～ 16 ％

B.21 ％～ 23 ％

C.41 ％～ 53 ％

D.71 ％～ 83 ％

A.15%～20%

B.20%～25%

C.25%～30%

D.30%～35%

A.20

B.50

C.80

D.100