It's the quiz's repeatedly saying "it's technically wrong" that irritated me.
We probably have to accept that whom is on its way out; it already is in spoken English unless you want to sound really stuffy. eg itre.cis.upenn.edu/~myl/languagelog/archives/001437.html
As has already been said, splitting infinitive is not wrong.
The less / fewer distinction has crept into English and is accepted by many educated people, but it's not as rigid as you might think. languagelog.ldc.upenn.edu/nll/?p=2819
dice is in the dictionary as an alternative singular noun for die.
Much as my inner pedant wants literally to mean "not figuratively", it's been used as an intensifier for a long time, eg by Dickens - examples are some way down this post: languagelog.ldc.upenn.edu/nll/?p=3007
You'll notice I'm a fan of Language Log, written by real linguists who actually look for evidence for grammar rules, not just insist on them because that's what their English teacher told them.