Jenni's 72-Year-Old Grandfather Has Difficulty Understanding Her When She Speaks,but

Jenni's 72-year-old grandfather has difficulty understanding her when she speaks,but he seems to understand her father much better.Why might this be?

A) People over 70 typically have difficulty with sounds over 6000 Hz.
B) People over 70 typically have difficulty with sounds over 9000 Hz.
C) People over 70 typically have difficulty with sounds over 12000 Hz.
D) People over 70 typically have difficulty with sounds over 15000 Hz.