Mark received a call on his cell phone from his mother, but the reception was so poor and there was ...

Mark received a call on his cell phone from his mother, but the reception was so poor and there was so much noise from the street that he had trouble making out her words. Even without knowing exactly what she was saying, however, he knew she was sad from her tone of voice. What can we infer from this information?
 
  a. Mark is unusually sensitive to people's moods. Most people cannot interpret emotions very well over the phone.
  b. Mark is probably mistaken about his mother's mood.
 c. It is likely that Mark was holding his cell phone up to his left ear.
 d. It is likely that Mark was holding his cell phone up to his right ear.