Linda and Betty were both twenty years old. They studied in the same medical college. In June, after a school year was over, they decided to take a vacation in the country. They went to several towns and villages, and visited some places of interest, saw and heard a lot of interesting things. They enjoyed themselves very much. One afternoon, they were going to stay overnight in a small town. It was too hot to go further and they wished they could find a river and swim in the cool water. They were driving the car slowly while they were looking around. Suddenly Linda saw a lake not far away. They drove there fast and stopped the car by the lake. They looked around and found a man was sitting on a stone and fishing there. When they took their clothes and were going to jump into the water, the man came up to them and shouted," Sorry, Madams' swimming is not allowed  in the lake!" "Why didn't you tell us about it before we took off our clothes?" Betty said angrily. "But it isn't to take off clothes by the lake," said the man. Linda and Betty were    _    .
classmates sisters doctors nurses