The original sentence, "The helper threw the trash in the dustbin," is in active voice. To convert it to passive voice, we need to make the object of the active sentence ("the trash") the subject of the passive sentence. The verb needs to be changed to a passive form, and the subject of the active sentence ("the helper") becomes the agent of the action, introduced by "by."

Let's analyze the options:

• Option 1: "The trash has been thrown in the dustbin by the helper." This uses the present perfect passive, implying the action happened at an unspecified time in the past and is relevant to the present. This doesn't accurately reflect the tense of the original sentence.
• Option 2: "The trash is thrown in the dustbin by the helper." This uses the present passive, suggesting a habitual or general action. This doesn't match the simple past tense of the original sentence.
• Option 3: "The trash had been thrown in the dustbin by the helper." This uses the past perfect passive, indicating an action completed before another past action. This is not the appropriate tense.
• Option 4: "The trash was thrown in the dustbin by the helper." This uses the simple past passive, which perfectly matches the tense and meaning of the original active voice sentence. The subject "trash" is acted upon, and the agent "by the helper" is clearly indicated.

Therefore, the correct answer is Option 4 because it accurately transforms the sentence into the passive voice while maintaining the original tense.