Jeremy Harmer in his book The Practice of English Languag...

A such errors as "she is more nicer than him" are part of a natural acquisition process among foreign learners; B

mistakes are subconsciously learnt and it is very difficult for a teacher to correct them;

C

when responding to errors, teachers should be seen as telling students off because they are wrong;

D

when second language learners make errors, they are demonstrating their difficulty in acquiring that language;

E

adults acquire a second language more easily than children because they are aware of grammar rules.