树木在环境保护中具有吸收二氧化碳产生氧气的重要作用。()
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Most propellers on merchant vessels are constructed of______．
A. manganese bronze
B. cast iron
C. mild steel
D. improved plow steel
Mean high water is the average height of ______.
A. the higher high waters
B. the lower high waters
C. the lower of the two daily tides
D. all high waters
国家法律规定，禁止在三十五度以上陡坡地开垦种植农作物。()
光源的光色呈现中间色的色温指数为 ()
A3500—5300K
B3300—5300K
C3300—5500K
D3500—5500K
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