消费不是（）的，消费者对一种商品的需求常常与对另一种商品的需求相关。 ["单一","习惯性","孤立","冲动性"]
有关脊椎动物的脊椎，下列正确的是（） ["由外胚层发育而来","在胚胎时期都呈现棍状结构，叫脊索","随动物的进化而形态上有所分化","不同种类，脊椎数目不同"]
Continuous sounding of a fog whistle by a vessel is a signal（）. ["that the vessel is anchored","to request the draw span of a bridge to be opened","of distress","that the vessel is broken down and drifting"]
简述军用小艇的特点。
熔融纺丝冷却长度受哪些因素影响？
生产中拉伸倍数如何确定？举例说明生产中如何实施？
