题目

The Japanese Macaca monkey has been studied in the wild for over 50 years. In 1952, on one small Japanese island, scientists dropped some 1 in the dirt for the monkeys. The monkeys liked their taste, but they found the dirt 2.One clever 18-month-old monkey found she could 3 the problem by washing the sweet potatoes in a nearby river. She taught this to her mother. Her 4 also learned this new way and they taught their mothers, too.All the younger monkeys 5 learned to wash the dirty sweet potatoes to make them 6 to eat. But many old monkeys found it very hard to learn this and still ate the 7 已知P为平面a外一点，直线la,点Q∈l,记点P到平面a的距离为a,点P到直线l的距离为b，点P、Q之间的距离为c，则 A.                                      B.c C.                                      D.