GRE Reading Comprehension: OG/PP2-GRE阅读OG/PP2 - 8594X7VWBSWU6S40P

It can be inferred from the passage that compared with other costs of singing, which of the following is true of the energy costs of singing? A. They are the single greatest cost to an individual bird. B. They have generally received more attention from scientists. C. They vary less from one bird species to another.