A、Watch for changes in weather. B、Watch their altitude. C、Check for weak spots in their balloons. D、Test the strength of the rop

Balloons have been used for sport for about 100 years. There are two kinds of sport balloons: gas and hot air. Hot air balloons are safer than gas balloons, which may catch fire. Hot air balloons are preferred by most balloonists in the United States because of their safety. They are also cheaper and easier to man age than gas balloons. Despite the ease of operating a balloon, pilots must watch the weather carefully. Sport, balloon flights are best early in the morning or late in the afternoon, when the wind is light. Over the years, balloonists have tried unsuccessfully to cross the Atlantic Ocean. It wasn’t until 1978 that three American balloonists succeeded. It took them just six days to make their trip from their homes in the United States to Paris, France. Their voyage captured the imagination of the whole world.