Preposition 10

 She opened her mouth so the doctor could look ______ her throat.

Prepositions are words that indicate relationships with the other words in the sentence. Prepositions of place are used to refer to a place, usually to denote the location of something or someone.

Let's look at the usage of various alternatives in the option as preposition of place:

 at : to refer to an exact place where something is situated / event

 on : to refer to placement of something attached / adjacent to something else; to refer to something displayed on something else

to : not used as a preposition of place

 for : not used as a preposition of place

In the sentence, as a reference to a specific location, I.e. "her throat". Therefore, the suitable preposition here is "at".

Thus, the correct complete sentence is:

She opened her mouth so the doctor could look AT her throat.