TOEFL Listening: TPO-TOEFL阅读TPO - 8PKDO40248C5L0_4N$

According to paragraph 5, which of the following is true about chemicals in buck rubs? A. They have to be at least two days old for females to be able to detect them. B. They are more effective in older buck rubs than in fresher ones. C. They may affect fertility in female deer. D. They can be more easily detected by young males than adult females.