这个创造性的设计，_____节约了石料，减轻了桥身的重量，______在河水暴涨的时候，______可以增加桥洞的过水量，减轻水对桥身的冲击。

①硫+氧气 $\stackrel{点燃}{\to }$ 二氧化硫

②碳+氧气 $\stackrel{点燃}{\to }$ 二氧化碳

③铁+氧气 $\stackrel{点燃}{\to }$ 四氧化三铁

通过比较，发现它们有许多共同点，请你写出其中三点：

①____；

②____；

③____．

短文改错

    My swimming experience is extreme interesting. There was a time when I swim like a rock.This went on till one day when I was fishing with a friend of mine at nearby pond. I was so much careless that I slipped into one. Had my friend not come to my rescue, I would have be drowned. Ever since then, I have come to know the importance of learn to swim. I didn't go to any training class but  learned it all by me. Now I have no difficult swimming at all . Though the way I swim looks clumsy ,at least it can keep me floating. Thinking of this, I feel quite satisfying.