问题详情

Why do researchers estimate elephant numbers in an area by counting dung piles.
A．Because elephants are difficult to catch.
B．Because it is not possible to count elephants from a plane.
C．Because it is not possible to keep track of elephants.
D．Because elephants are shy animals. 此题为多项选择题。请帮忙给出正确答案和分析，谢谢！