Answer: Option B
The most appropriate preposition in this sentence is "for". The sentence "The insects are a great nuisance for us" indicates that the insects are causing trouble or annoyance for us.
Explanation:
To determine the correct preposition, it is important to understand the meaning and context of the sentence. In this case, the sentence describes insects that are causing a nuisance for us. The preposition "for" is the most appropriate choice because it is used to indicate the purpose or reason for something, or the person or thing that something is intended to benefit or harm.
Here are some relevant definitions and examples of the preposition "for":

• "For" is used to indicate the purpose or reason for something. Example: "I bought this book for my sister's birthday."
• "For" is used to indicate the person or thing that something is intended to benefit or harm. Example: "He opened the door for the old woman."
• "For" can also be used to indicate a period of time. Example: "I will be on vacation for two weeks."

Other prepositions such as "with", "to", "at", and "upon" do not convey the same meaning as "for" in this context.

• "With" is used to indicate association or accompaniment. Example: "I went to the party with my friend."
• "To" is used to indicate direction or destination. Example: "I am going to the store."
• "At" is used to indicate a specific location or time. Example: "I will meet you at the park at 3pm."
• "Upon" is used to indicate a moment of time, or a specific event or situation. Example: "Upon hearing the news, she burst into tears."

In summary, the correct preposition in this sentence is "for", as it indicates the purpose or reason for the insects being a nuisance for us.