An arithmetic progression P has first term p and common difference d, while an arithmetic progression Q has first term q and common difference e. If their nth terms are equal for some positive integer n, which equation correctly expresses this condition?
a) p+nd=q+(n−1)e
b) p+nd=q+ne
c) p+(n−1)d=q+(n−1)e
d) p+(n−1)d=q+ne