6个伸长节间的品种最上3个发根节位的发根期处于()。 ["倒6叶至倒2叶期;","倒5叶至倒1叶期;","倒4叶至孕穗期;","倒3叶至抽穗期;"]
电缆转弯应均匀圆滑,弯弧外部应保持垂直或水平成直线,电缆转弯的最小曲率半径应大于()。 ["A、20mm","B、30mm","C、40mm","D、50mm"]
滚扣眼布采用布料的方向为() ["直料","斜料","横料"]
光纤跳线在机架内应作盘留,盘留长度≥0.4m,盘留曲率半径应≥()。 ["A、20mm","B、30mm","C、40mm","D、50mm"]
烫省从()向()烫。 ["A.省根;左","B.省根;省尖","C.省左;省尖","D.省侧;省尖"]
果树种质资源按来源分为几类?各类有何特点和作用?