儿童多动症最主要的临床表现是（） ["注意缺陷","活动过多","学习困难","品行问题","易冲动"]
乙类项目管理单位必须具备以下基本条件，在册建设管理人员不少于（）人 ["30","35","40","45"]
What are two important considerations when using 2- or 4-channel 15216 OADMs？（） [" All "Add" channels require uniform power levels."," The flexibility of wavelengths per OADM is limited."," It is easier to balance "Pass-Through" and "Add" channels."," There is lower pass-through loss using multi-channel OADMs."," You can extract a single channel without dropping other channels."]
关于儿童多动症，下列描述错误的是（） ["患儿存在明显注意力集中困难","与遗传因素有关","患儿多有神经系统发育不成熟","女孩多于男孩","宜采用综合性治疗方法"]
以下可以作为双桥并联整流系统的整流变压器是（）。 ["一台接线组别为D，d的双绕组变压器；","二台接线组别为Y，y的双绕组变压器；","一台三绕组变压器，二次绕组接线组别分别为y和d；","一台三绕组变压器，二次绕组接线组别分别为y。和y"]
简述类的字段和属性的区别。
