Amen to that.
懂 also means understand, why can it not replace 明白?
It can, we need to report this.
It can. If it marked you wrong, report it.
I thought that 东西 was for tangible physical "things" and 事情 was for intangible "things" like ideas. Should 地理很难，我不明白很多事情 be correct?
“地理很难，我学不明白很多东西” should also be a translation for it.