**The Active Voice of "A Snake was Killed by the Farmer"**

The active voice of the sentence "A snake was killed by the farmer" would be "The farmer killed a snake." In the active voice, the subject performs the action directly, while in the passive voice, the subject receives the action.

**Explanation:**

1. **Subject and Verb Placement:**
- In the given sentence, "A snake was killed by the farmer," the subject is "a snake" and the verb is "was killed."
- In the active voice, the subject, which is the doer of the action, comes before the verb.

2. **Transformation from Passive to Active Voice:**
- To convert the given sentence from passive voice to active voice, we need to identify the subject, which is performing the action, and place it before the verb.
- The subject in the given sentence is "the farmer," and the verb is "killed."
- Therefore, the active voice of the sentence is "The farmer killed a snake."

3. **Impact on Sentence Structure:**
- Switching from the passive voice to the active voice often results in a change in sentence structure.
- In the original passive sentence, the subject "a snake" receives the action and is placed at the beginning of the sentence.
- In the active voice sentence, the subject "the farmer" performs the action and is placed before the verb.

4. **Clarity and Directness:**
- Using the active voice generally makes sentences clearer and more direct since the subject is responsible for the action.
- The active voice emphasizes the doer of the action, which in this case is the farmer who kills the snake.

In summary, the original passive sentence "A snake was killed by the farmer" is transformed into the active voice as "The farmer killed a snake." This change results in a more direct and clearer sentence structure, where the subject performs the action instead of receiving it.

The farmer killed the snake.