右图为钠元素的原子结构示意图，下列说法不正确的是 A．钠原子核外有三个电子层

螺旋机构是（）与（）配合将旋转运动变为直线运动的机构。

Both bus and tree topologies are characterized by the use of multipoint(1)．For the bus,all stations attach,through appropriate hardware(2) known as a tap,directly to a linear transmission medium, or bus. Full-duplex operation between the station and the tap allows data to be transmitted onto the bus and received from the(3).Atransmission from any station propagates the length of the medium in both directions and can be received by all other(4).At each end ofthe bus is a(5),which absorbs any signal, removing it from the bus．

空白（3）处应选择（）

A.tree

B.bus

C.star

D.ring

颅底型脑膜脑膨出自颅内疝出的部位是（）。

A.筛骨筛板

B.筛骨筛顶

C.眶上裂

D.筛骨鸡冠前方的盲孔

E.筛骨鸡冠之后

细菌耐药最常见的机制是（）

A.产生抗生素灭活酶

B.抗菌药物作用靶位改变

C.细菌改变代谢途径

D.细菌细胞膜渗透性改变，使抗菌药物不易进入细菌细胞

E.细菌细胞将抗菌药物排除细菌

采煤工作面上隅角采用风筒导引瓦斯时，风筒内的瓦斯浓度应（）。

A.在1.5％以下

B.不超过1.5％

C.在3.0％以下

D.不超过3.0％