题目

Washing habits have changed over the years. In the 16th century, most people had a bath once a month...if they were lucky. Up until the 1950s, it was once a week. Only just recently has the concept of daily showering become popular.But now, according to the New York Times, things are changing again.The latest trend is known as “soap­dodging”. It basically consists of washing less, having fewer showers and using less soap.“I just wash my hair once a month now, ” said Brett Dawson, a 32­year­old management consultant.“I have just one bath a week,” said Miriam Bayliss, a 28­year­小明在实验室用排空气法制取氧气时，导管未插到集气瓶底部，发现实际得到氧气180mL，已知集气瓶的体积为200mL，求集气瓶中未排净的空气体积？（氧气在空气中的体积分数为15）