铁牛—55型拖拉机双作用离合器工作特点是：当踏下踏板第二行程时，（）。A、主离合器

读我国近海某区域11月份多年平均表层盐度（‰）平面分布图，回答问题。

（1）该区域11月份表层盐度的分布特点是________。

（2）影响盐度分布的因素有哪些？

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（3）图中表层等盐度线的走向有何特点？甲处海水盐度（26．94‰）较低的原因是什么？

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单句填空：

小题1:Dr Yuan___________________ his life. However, he doesn’t care about being famous.

小题2:Why not study at medical college like Lin Qiaozhi and _________ her good work?

小题3:She spent years _________ and recording chimps’ daily activities

小题4:She has argued that wild animals should________ and not used for entertainment or advertisements.

The coffee is wonderful! It doesn't taste like anything I _____ before. [ ]

A. was having

B. have

C. have ever had

D. had ever had

煤炭是可燃的有机物与不可燃的无机物的混合物。

龈牙组纤维

A．纤维起于牙槽嵴顶，呈放射状向牙冠方向走行，止于牙颈部的牙骨质
B．自牙颈部牙骨质，向牙冠方向散开，广泛地位于牙龈固有层中
C．自牙槽嵴向冠方牙龈固有层展开，止于游离龈中
D．起自根分叉处的牙根间骨隔顶，至根分叉区牙骨质
E．自牙颈部的牙骨质，越过牙槽嵴，止于牙槽突骨密质的表面