题目

In the hills outside Missoula, Montana, wildlife biologists are looking at how climate change affects something very small: the snowshoe hare. Life for snowshoe hares is pretty stressful-almost everything in the forest wants to eat them. Alex Kumar, a graduate student at the University of Montana, lists the animals that are hungry for hares. “Lynx(山猫), foxes, coyotes(土狼),[… even] red squirrels(松鼠).” Kumar and field technician Tucker Seitz spend months searching these woods for hares, often listening for signals from hares they’ve already put radio collars(项圈) on. �16．$\overrightarrow{OA}$-$\overrightarrow{OD}$+$\overrightarrow{AD}$=$\overrightarrow{0}$．