In the food chain you have just described, mice are the snakes main/only food source. If mice become extinct, the snake population will decrease until the point where they die out, if no other food source is found.
Answer:
![\boxed{\bf~D,~if~no~other~food~source~is~found~snakes~will~die~out}](https://img.qammunity.org/2019/formulas/biology/high-school/eve9pn6pr15931l0tlp4t2pqlqrz4tsykv.png)
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