稚蚕专用桑园,桑品种要求栽培() ["A.发芽势强","B.成熟早","C.成熟度齐","D.叶质充实的早熟桑"]
单位叶面积在单位时间内干物质增量,用下式表示()。 ["(1/W)(dw/dt)","(1/A)•(dw/dt)•","(1/L)(dw/dt)","(L/W)•"]
棉的特征?
水样冷却器应能保证水样流量达()ML/MIN。 ["A、300","B、400","C、500~700","D、800"]
单主梁门式起重机和装卸桥门架当跨度S≤26m时,其跨度S的最大允许偏差为()mm。 ["A、±7","B、±8","C、±9","D、±10","E、±3","F、±5","G、±6","H、±12","I、±4","J、±1"]
何谓酸性焊条和碱性焊条?二者有什么区别?