Hmmmm . . .
Quick visit today:
1. 'of itself' and 'by itself' are both correct, but 'of itself' is an older structure. Prepositions love to sneak around in English, and come into and go out of fashion. Patience!! Here are a couple of examples: Australians say, 'out the back of the house,' but Americans say, 'in back of the house' -- that 's a modern difference. My answer is an example of a preposition ('of') which has been dropped from use, and 'replaced' with another ('by'). You will find the expression 'to treat of,' which means 'deal with,' in Victorian novels; but you'll never hear or see it now.
Learn the principle of praxis, and issues like this will make sense -- more sense!
2. 'We still lag behind . . . ' -- present simple tense of 'lag,' or 'We have fallen behind . . . ' -- present perfect tense of 'fall.'
3. I think 'logic' is correct -- beware, though: perhaps the assessor is looking for that evil creature collocation!! ('hue and cry,' 'let and hindrance')
4. Hmmm . . . They seem synonymous to me. However, look them both up in a thesaurus; and see if they ARE listed as synonyms. Then, look them both up in a good dictionary – a dictionary that provides etymological details – and see if their etymologies give you any clues.
Gotta go. See you soon.
Student or Learner