封闭环公差等于（） ["A、各组成环公差之差 ","B、各组成环公差之和 ","C、增环公差 ","D、减环公差"]
调质即是（） ["A、淬火＋高温回火 ","B、淬火＋中温回火 ","C、淬火＋低温回火 ","D、渗碳＋淬火"]
Ｔ10Ａ钢锯片淬火后应进行（） ["A、高温回火 ","B、中温回火 ","C、低温回火 ","D、球化退火"]
熔断器具有（）保护作用 ["A、过流 ","B、过热 ","C、短路 ","D、欠压"]
机床照明灯应选（）Ｖ电压 ["A、6 ","B、24 ","C、110 ","D、220 "]
退火的目的
