为了便于维护保养留有足够的维修保养空间和通道，一般人行通道宽度≥（）m。
A. 0.7
B. 0.5
C. 0.6
D. 1.0
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如下图系谱中性状的遗传方式为常染色体显性遗传，第二代第二个个体表现正常，其原因属于：（）
A. 表型模写
B. 外显不全
C. 表现度变化
D. 基因互作
Oneofthedisadvantagesofusingcarbondioxidetoextinguishafireinanenclosedspaceis（）.
A. the"snow"whichissometimesdischargedalongwiththegasistoxic
B. prolongedexposuretohighconcentrationsofC0gascausessuffocation
C. rapiddissipationoftheC0vapor
D. theC0gasislighterthanairandalargeamountisrequiredtoextinguishafirenearthedeck
Recordsofgarbagedisposalarerequiredtobemaintained（）.
A. untileachquadrennialPSCinspection
B. untiltheendofeachvoyage
C. foraminimumofoneyear
D. foraminimumoftwoyears
Atankwhichhasbeensealedforalongperiodoftimecanbedangerousbecause（）.
A. steelsurfacesconsumeoxygenbyrusting
B. sealedtanksusuallyformavacuum
C. moisturecondensesinthetank,displacingtheoxygen
D. mosttankcoatingsgiveoffpoisonousvaporsinthepresenceofmoisture
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