Researchers Have Claimed That the Average Number of Headaches Per $n = 16$

Researchers have claimed that the average number of headaches per student during a semester of Statistics is 11. Statistics students believe the average is higher. In a sample of $n = 16$ students the mean is 12 headaches with a deviation of 2.4. Which of the following represent the null and alternative hypotheses necessary to test the students' belief?

A) $H _ { 0 } : \mu = 11$ vs. $H _ { \mathrm { a } } : \mu > 11$
B) $H _ { 0 } : \mu = 11$ vs. $H _ { \mathrm { a } } : \mu \neq 11$
C) $H _ { 0 } : \mu < 11$ vs. $H _ { \mathrm { a } } : \mu = 11$
D) $H _ { 0 } : \mu = 11$ vs. $H _ { \mathrm { a } } : \mu < 11$