题目

       When was the last time you relied on an old-fashioned map to figure out the route to an unfamiliar place? For many, the GPS has revolutionized navigation, making a paper map almost obsolete? So how has this piece of technology developed over its 26 years of existence? On February 14,1989,the first satellite in the US Global Positioning System was sent into space from Cape Canaveral, beginning the start of one of the wonders of the modern world.        GPS stands for Global Positioning System, which is made of a network of around 30 satellites that move around the ear13. ___ had they reached the 30th floor ____ they realized that they had forgotten to take the key.A．Hardly; than B．Hardly; whenC．No sooner; when D．No sooner; then