关于下列四幅图的说法，正确的是（   ）

线段有两个端点。

   People are often killed while c____  the road. Most of them are old people and c____ . Old people are often killed because they are careless. People should look and listen b____  they cross the road. A car, a truck or a bus can't stop very q____ if it is going very fast. It will travel many meters before it s____ . Pedestrian(行人)don't know this. They think that a car can stop right away. It is h____ for a pedestrian to know how fast a car is traveling. The only s____ way to cross the road is to look at b____ ways, right and left. The correct way to cross the road is t____  walk quickly when the traffic l____ turn green.

人体内某一细胞正在进行减数分裂，其内有44个常染色体与两个X染色体，此细胞不可能是（　　）

①初级精母细胞   ②次级精母细胞   ③初级卵母细胞   ④卵细胞．