An idiomatic expression is a type of informal English where the meaning
of the expression is different than the literal meaning of the
expression.
Option A: The idiom 'looking down on others' means 'to regard oneself as superior to others and hence act in a snobbish manner'. It is relevant to the phrase that follows "holier-than-thou attitude!" which is similar in meaning. Hence A is correct.
The phrases 'annoying others', 'asking questions' and 'preaching good things' all have a literal meaning; they are not idiomatic expressions. Hence options B, C and D are incorrect.