Sentence Correction

Hello Guys

I have been studying SC very closely from OG 12 and have revised it twice.
While revising I realized that many of the questions which I got wrong are the same as my mistakes during first attempt. Funny!

Anyways, I have understood the explanation for most of them except for the following. Tenses still remain a critical area for me!

Note: I've made notes either of the answer choice which I feel should be right or if an explanation of a particular concept is required:

Q19: Funda of sub ordinate clause is not clear.
Q26: In the (E) choice - which is used to add non essential information?
"Which" creates a lot of confusion in my mind when ever I encounter it
Q30: I'm not convinced with the usage of word Protecting
Q33: Explanation for choice B required
Q51: didn't understand the question and explanation as well
Q57: What's explanation for using "that" as subordinate clause?
Q59: the use of comma is not clear to me, I do understand the purpose of "for"
Q63: why not which, what's the funda to not use it. It's same which problem ???

How and when do you use absolute phrases? (I read it from Manhattan SC but not very clear)

Any input is always welcome!

Best
VM