The Butterfly Effect is an allegory, example or metaphor devised by Edward Lorenz to help explain Chaos Theory to a wider audience.
Chaos Theory is a branch of mathematics which deals with situations that arise when small differences in initial conditions result in widely different final results. This doesn't mean that anything can happen but does mean ...
In the first example, the "statement" is that "the internet works as a contemporary CV". The writer thinks that it is obvious that this statement is true.
As to your second example, the words "form of lengthy" don't belong together. The book "makes demands of its reader". What form do these demands have? "Lengthy exercises to be done". (The word "lengthy" ...
It might be considered correct (but awkward, unless it is in poetry) if you added a comma after "Scary".
As it stands, the first time one reads it, it's too easy to read "Scary looks" as the subject of the sentence and then stumble looking for the non-existent verb.
I believe the teacher is incorrect. There are possibly two interpretations of what the author is speaking of:
they had a friend who had several phone numbers, one of which they lost
they have several friends, and lost the phone number for one of them
The clue to the correct interpretation is that phone number is singular rather than plural, indicating ...