____ the distance was too far and the time was short, we decided to fly there instead of going ...

考查分詞做狀語。Discover與主語we之間構成主動關系，故使用現在分詞做狀語。句意：當我們發現距離太遠，時間太遠的時候，我們覺得坐飛機去那兒，而不是坐火車。故A正確。