单选题 Last week, France announced that the country would pave 621 miles of road with solar panels over the next five years, with the goal of providing cheap, renewable energy to five million people. Called "the Wattway," the roads will be built through joint efforts with the French road-building company Colas and the National Institute of Solar Energy. The company spent the last five years developing solar panels that are only about a quarter of an inch thick and are strong enough to stand up to heavy highway trafiwithout breaking or making the roads more slippery. [4]The panels are also designed so that they can beinstalled directly on top of existing roadways, making them relatively cheap and easy to install. Question:What was France's purpose of constructing "the Wattway"