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
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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
轮距越大，对桥吊的稳定性越有利，轮压（）。
A. 不变
B. 加大
C. 降低
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