Concept:
The preposition
with is used to indicate the instrument or tool used to perform an action.
Step 1: Understand the sentence.
The sentence tells us that a bird was shot using an airgun.
The airgun is the instrument employed to perform the action.
Step 2: Rule of usage.
When a tool, instrument, or weapon is used, the preposition
with is generally used.
Examples:
• He cut the paper with scissors.
• She wrote with a pen.
• The hunter shot the animal with a rifle.
Step 3: Analyze the options.
By indicates agency.
For indicates purpose.
In indicates location.
Only
with correctly expresses the instrument used.
Step 4: Conclusion.
The correct sentence is:
He shot a bird with an airgun.
Hence, option (B) is correct.