Select the sentence with the appropriate use of preposition.

Correct option is D

Option (d) is the correct answer: "Children are fond of sweets."
 The preposition "of" is used to show possession or relationship between two nouns. In this sentence, "children" is the subject and "sweets" is the object of the preposition "of". The preposition "of" indicates that the children have a fondness for sweets.
 Option (a) is incorrect because the preposition "to" is not appropriate in this context.
 Option (b) is incorrect because the correct preposition to use after "fond" is "of", not "off".
 Option (c) is also incorrect because "with" is not the appropriate preposition to show the relationship between "children" and "sweets".