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

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 1000 Hz.
B) People over 70 typically have difficulty with sounds under 3000 Hz.
C) People over 70 typically have difficulty with sounds over 6000 Hz.
D) People over 70 typically have difficulty with sounds under 6000 Hz.