Question

You should avoid...

Answer 1

#1 is incorrect because concise language involves using to-the-point, non-fluff language and vocabulary to get one's ideas across--this is obviously necessary for effective writing.

#2 is incorrect because concrete nouns are simply physical nouns that aren't abstract, such as "I", "You", "Michael", "Table", "Cat".  Concrete nouns are obviously used effectively in writing constantly.

#3 is incorrect because these expressions are formal rather than informal and will therefore fit well into most academic writing.

#5 None of the above is therefore correct.