The correct option is C The staff was friendly towards us.
Predicative adjectives are placed after the noun, but not
immediately after it; rather, it follows a linking verb that is placed after
that noun, for example, 'I love red', where 'red' is the adjective that is used predicatively and is placed after the linking verb, 'love'.
Option A is correct as the adjective "friendly" modifies the noun "staff" and is placed after the linking verb "was".
Option B is incorrect because the adjective is not linked to the verb here, but it comes after the object "us". Also, an adjective does not precede an object that it modifies.
Option C is incorrect because adjectives do not precede articles ("The") in the normal order of words.
Option D is incorrect because the answer lies in A.