Each of the following four sentences has two words within brackets. The word which has been highlighted has been used as the most appropriate word for the sentence. In one of the sentences, the wrong word has been highlighted. Identify that sentence and indicate that option

Let's have a look at the meanings of each of the words.
Complemented: A thing that contributes extra features to something else in such a way as to improve or emphasize its quality.
Complimented: A polite expression of praise or admiration
A compliment which means a polite expression of praise is used correctly in the sentence.
Beneficent:(of a person) generous or doing good.
Beneficial: Resulting in good; favourable or advantageous
A rule can be beneficent. Hence beneficial was misused in the sentence.
Oversight: An unintentional failure to notice or do something.
Oversite: A layer of concrete used to seal the earth under the ground floor of a house
An oversight which means failure to notice is used correctly in the sentence
Break: Fail to continue with 
Brake: A device for slowing or stopping a moving vehicle
A break which means failure to continue is used correctly in the sentence.

Hence B is the correct answer.