光纤由3层材料组成，中间层的作用是（）。 ["信号地","增加抗拉强度","防止光折射","保护作用"]
The （） in the steering gear system provides the force. ["control equipment","power unit","transmission mechanisms","fittings and pipeline"]
安全含水量低、种粒很小的种子用普通干藏法贮藏。
In the doldrums you can expect（）. ["steady，constant winds","frequent rain showers and thunderstorms","steep pressure gradients","low relative humidity"]
商标印制单位在承接商标印制业务时，对商标印制委托人提供的有关证明文件及商标图样，商标印制业务管理人员应当严格核查。（）
造成变压器不对称运行的原因有哪些？
