Anormal distribution curve, where x = 70 and σ = 15, was created by a teacher using her students’ grades. what information about their performances can be obtained by analyzing the curve?

The curve is a normal distribution curve where x = 70 and σ = 15. The variable x is the mean of the students' grades which is equal to 70. The standard deviation is 15, the actual mean is 70+-15. A normally distributed curve means that most of the students got mostly 75. 

Ithink it’s b because it say 3 plastic rings and all the balls