Fill in the blank with the most appropriate preposition.
The patients in the hospital are looked after ___ the nurses.
A) By
B) At
C) To
D) Into

Hint: A preposition is a word or phrase that precedes a noun, pronoun, or noun phrase to indicate direction, time, place, location, spatial relationships, or to introduce an object. Prepositions include words like "in," "at," "on," "of," and "to." The location or timing of something in relation to something else is defined by prepositions.

Complete answer:
- Prepositions show how other words in a sentence are related.
- Many prepositions indicate the location of something or the time it occurred.
- Since most prepositions have several meanings, their interpretation varies greatly depending on the context.
- It is not a grammatical mistake to end a sentence with a preposition.

Now let us look at the options:
Option A) By: This is the correct option. The word 'by' is used to denote who is performing the action or to convey proximity. The operation 'looked after' is performed by the 'nurses' in the given sentence.
Option B) At: This option is incorrect because the preposition ‘at’ is used to indicate a position or timing whereas in this sentence we have to show action.
Option C) To: This option is incorrect because the preposition ‘To’ is used to denote a connection, movement, or direction of something which is not required in the above sentence.
Option D) Into: This option is incorrect because the preposition 'into' refers to the transfer of something from one location to another which is not required in the above sentence.

Thus, the correct answer is Option A.

Note: Direction, time, place, and spatial relationships, as well as other abstract types of relationships, are all indicated by prepositions.
- Directions: Our destination can be found to the left.
- Time: Since this morning, we've been working.
- Location: We saw a movie at the theatre.
- Space: The dog hid under the table.