What do we call a sharp, flat, or natural sign that raises or lowers a note in a measure?

a. key signature

b. staff

c. accidental

d. accent mark

Monthly water bills for a city have a mean of $108.43 and a standard deviation of $32.09. find the probability that a randomly selected bill will have an amount greater than $155, which the city believes might indicate that someone is wasting water. would a bill that size be considered unusual?