问题详情

According to paragraph 1, what was a common claim about ecological communities before the early twentieth century？

A．Every species in a community has a specific role in that community.

B．It is important to protect communities by removing certain species.

C．A precise balance is difficult to maintain in an ecological community.

D．It is necessary for new species to be added quickly as ecological communities develop.

请帮忙给出正确答案和分析，谢谢！