有几题高三的短文题词不明白,希望有人进来认真看完解析.

有几题高三的短文题词不明白,希望有人进来认真看完解析.
When the New Year (bell) sounds,fireworks and crackers begin to explode here and there ,which last 3 hours.
Bell 在这句到底怎么翻译》》》这个用法怎么这么奇怪?
We hope we will have more activities like this (held) in our school.
为什么用held不是Hold跟虚拟有关吗?详细说说没明白彻底
Besides,over 15％ more students become (mentally) unhealthy.
为什么用mentally不是mental为什么要用adv形式?
I am sure that i am fit for the job (needed) in your company.
为什么用ed形式?原因?
After (graduating) from a middle school ,i learned English language.
我知道After是介词,这里是介宾的原因.可是我想表达是毕业以后用ed形式为何不行呢?
They were (mostly) 大多数color photos,but some are black-and-white ones.
为什么用mostly这个是副词呀?

好的 很无厘头的问了这样的问题,因为这些都是短文填词中错误的,文章太长不可能都打呀?所以把错误的打出来了,希望你可以耐心的看,针对我的疑问回答,