'Idiomatic expressions are a
type of informal English that have a meaning different from the meaning
of the words in the expression.'
The
phrase "is quite loud and clear" is an idiomatic expression. It means
'very clear and easy to understand'.
Option A also contains the same meaning, that the principle's message was clear and definite. Hence A is the correct option.
Option B is incorrect because this gives the literal meaning of the idiom.
Idioms are not literal in meaning.
Options C and D give meanings which are irrelevant to the sentence. The 'authoritative manner' and 'arrogance' are not
implied by the idiom.
Hence, options C and D are incorrect.