The question is asking us to select the correct preposition to complete the sentence: "He was looking _ _ _ _ _ _ all the different possibilities."
The options given are:
To determine the correct preposition, we need to understand the context and common usage of prepositions within English grammar. In this sentence, the phrase "looking for" is commonly used to express the action of searching or trying to find something. Therefore, "for" is the correct preposition to complete the sentence.
Let's look at why the other options are not suitable:
Therefore, based on the standard usage of prepositions for expressing a search, the correct answer is for.