The Decline in Approximately 70% of the World's Bird Species

Multiple Choice

The decline in approximately 70% of the world's bird species is particularly alarming to scientists because ____ .

A) this is the first time any bird species have been threatened with declining numbers
B) the cause is a non-human activity that scientists cannot determine
C) only land birds are affected, while water birds seem to be maintaining normal population numbers
D) birds are excellent environmental indicators
E) bird watching now generates a significant portion of tourist dollars in some countries