作物栽培学中将作物分为（）作物、经济作物、（）作物。

什么是作物栽培学？

简述作物栽培学的性质和任务。

简述烟草地膜覆盖栽培技术。

作物栽培业的（），决定了作物栽培学这门科学的内容不但十分丰富，而且需要不断充实和更新。

Every deliberate act of wrongdoing by the master or any of the crew against the ship or cargo，without the authorization or privity of the Shipowner or his agent，is（）.

（）, or drum is used for hauling in or letting out the wires or ropes which will fasten the ship to the shore.

A salvor may be（）the whole or part of the payment due under Salvage Convention to the extent that the salvage operations have become necessary or more difficult because of fault or neglect on his part or if the salvor has been guilty of fraud or other dishonest conduct.

逻辑运算符（AND、NOT、OR）的运算顺序是AND→OR→NOT。

简述烟草栽培面向21世纪发展对策

诱变育种宜选用作基础材料的有（）。

逻辑运算符（AND、NOT、OR）的运算顺序是AND→OR→NOT。