一瓶浓度为80%酒精溶液倒出<img style='vertical-align:middle' src="https://www.bestkids.net/android-static/%E5%85%AC%E5%8A%A1%E5%91%98/8987246cbb714076bd496d8646b0b8e5.001.png" width="15" height="41" alt="">后再加满水，再倒出<img style='vertical-align:middle' src="https://www.bestkids.net/android-static/%E5%85%AC%E5%8A%A1%E5%91%98/8987246cbb714076bd496d8646b0b8e5.002.png" width="16" height="41" alt="">后仍用加满，再倒出<img style='vertical-align:middle' src="https://www.bestkids.net/android-static/%E5%85%AC%E5%8A%A1%E5%91%98/8987246cbb714076bd496d8646b0b8e5.003.png" width="15" height="41" alt="">后还用水加满，这时瓶中溶液的酒精浓度是（　）