Fill in the blank with the most appropriate word.
I took my car to the garage _____ this morning.
a. in
b. when
c. *
d. at

Hint: Read the given sentence and understand what it means. Now, go through the options and recall what each of them signify. You can use the ‘Hit and trial’ method to check which of the options fit the context of the sentence.

Complete answer: In this question, it will be helpful for the student to recall the concept of prepositions. A preposition is a function word that combines with a noun or pronoun or noun phrase to form a prepositional phrase that can have an adverbial or adjectival relation to some other word.
Let us analyze the options given to us in this question -
Option (a.), 'in', refers to ‘Contained by’.
Therefore, option (a.) is incorrect as it is a preposition. A preposition has already been used in the sentence, thus, another is not needed.
Option (b.), ‘when', refers to ‘At such time as’.
Therefore, option (b.) is incorrect as it is a preposition. A preposition has already been used in the sentence, thus, another is not needed.
Option (c.), ‘*', refers to putting no word in the given blank.
Therefore, option (c.) is correct as the given sentence fulfils all grammatical rules in itself.
Option (d.), ‘at', refers to ‘In or very near a particular place’.
Therefore, option (d.) is incorrect as it is a preposition. A preposition has already been used in the sentence, thus, another is not needed.
Therefore, option c is correct.

Note: Prepositions have no particular form. The majority of prepositions are one-word prepositions, but some are two- or three-word phrases known as complex-prepositions(according to, but for, in spite of, on account of).