下列有关分子、原子、离子的说法错误的是（　　）
①分子、原子、离子都是构成物质的粒子。②只有分子、原子可以保持物质的化学性质。③原子、离子都是由质子、中子和电子构成的。④离子也可以得失电子变成原子。⑤原子是化学变化中的最小粒子，所以原子肯定不能再分。⑥化学变化的实质：分子破裂成原子，原子重新组合成新分子。⑦原子的种类由质子数或核电荷数决定。 ⑧原子的质量主要集中在原子核上

根据文意及首字母提示补全短文。

    How can we students keep ourselves safe? Here are some tips.

    On your way home or to school: Wait for the g____ traffic light, and look left and right before you cross the road. If you see a car coming, don't cross until it really s____. Dress in bright colours so that the drivers can see you c____.

    At school: When students around you begin to push, try to hold onto something, or stay in a safer corner. If you f____ down in a crowded place, cover your head w____ both hands.

    When there's a fire: Stay calm and leave quickly. Use a piece of wet cloth to cover your mouth and nose so that you don't breathe in s____. If your clothes catch fire, drop to the ground and roll from side to side to p____ out the fire.

    For eating: Wash f____ like apples or pears carefully before you eat them. Check the expiration dates（保质期）and if your food looks or smells b____, don't eat it.

    For riding on the escalator(自动扶梯)：Hold onto the handrails (扶手）and stand on the right side of the escalator because right arms are stronger. It is d____ to run up and down on it. You may fall down because escalator steps are not designed for running.

阅读有关江苏省城市化发展的材料，回答下列问题。

材料一：改革开放以前，在计划经济条件下，受严格的户籍制度影响，江苏省城市人口的增长主要来源于自然增长，城乡之间的人口流动基本处于停滞状态。下图表示这一时期江苏省城市化进程。

材料二：1978年实施改革开放政策以来，江苏省成为我国经济增长最快、最具活力的省区之一。20世纪80年代苏南地区的乡镇企业迅猛发展，被誉为“苏南模式”。  下图表示这一时期江苏省城市化进程。

材料三：见下图。

钢铁制造的船能够浮在水面上，原因在于它____很大。