错收是指收进（）的秘密载体，且已出局者。 ["A、超重","B、明显不符合“寄递范围”","C、书写有误","D、收件单位不够级别"]
双梁通用门式起重机和装卸桥主梁上拱度最大值应处在主梁跨中部（）范围内。 ["A、S/10","B、S/15","C、S/20","D、S/25","E、S/5","F、S/3","G、S/4","H、S/6","I、S/2","J、S/7"]
低产桑园的改造措施有（） ["A．压条补株","B．壮苗补缺","C．提高剪定","D．套种更新"]
作物群体中CO2浓度最高的时期是（）。 ["中午","午夜","凌晨","傍晚"]
表明蚕处于求食状态的有哪些？
什么是天丝纤维？
