What is the 15th letter of the English alphabet?

A. O

What is the 10th letter of the English alphabet?

A. J

How many times does the letter 'A' appear in the series: A, B, A, C, A, D, E?

B. 3

If the letter 'M' is the 13th letter, what is the 15th letter?

B. O

In the series A, B, C, D, E, F, G, H, I, J, how many letters come before the letter 'E'?

B. 4