Normal Probability Distributions:Completely stumped

A teacher informs her class that grades will be curved. Scores for the test are normally distributed with a mean of 25 and a standard deviation of 5..

A: Top 10% (This is the only answer I have gotten)

B: Scores above the bottom 70% & below the top 10%

C: Scores above the bottom 30% & below the top 30%

D: Scores above the bottom 10% & below the top 70%


I would greatly appreciate any help....

Thank you in advance...

What tools do you have? Is there a table? Can you use your calculator? Do you understand the symmetry of the Normal Distribution? How did you arrive at the one answer you managed? Why doesn't whatever you did work for the others?

Give a clue, please.