Read the following article and select the best answer. Article: There was once a man called Mr. Flowers, and flowers were his only joy in life. He spent all his spare time in one of his four glass-houses and grew flowers of every color, with long and difficult names, for competitions, he tried to grow a rose of a new color to win the silver cup for the Rose of the Year. Mr. Flowers' glass-houses were very close to a middle school. Boys of around thirteen years of age were often tempted to throw a stone or two at one of Mr. Flowers' glass-houses. So Mr. Flower did his best to be in or close by his glass-houses at the beginning and end of the school day. But it was not always possible to be on watch at those times. Mr. Flowers had tried in many ways to protect his glass, but nothing had been useful. He had been to report to the headmaster, but this bad not done any good. He had tried to drive away the boys when they threw stones. He had even picked up all the stones around his garden, so that the boys would have nothing to throw, but they soon found others. At last Mr. Flowers had a good idea. He put up a large notice. It was made of good, strong wood. It was some meters away from the glass-houses. On it he had written the words: DO NOT THROW STONES AT THIS NOTICE. After that, Mr Flowers had no further trouble: The boys were much more attempted to throw stoned at the notice than at the glass-houses. Question: Mr Flowers stayed in or close by his glass-houses _ - at times when school-boys were walking near them - all the school day when there were no boys around - where he could not be seen by the boya passing - in his spare time at the beginning and end of the school day
at times when school-boys were walking near them