Same setup. Speed of current = ?

• a$\dfrac{d}{2}\left(\dfrac{1}{q} - \dfrac{1}{p}\right)$
• b$\dfrac{d}{2}\left(\dfrac{1}{p} - \dfrac{1}{q}\right)$
• c$\dfrac{d}{2}\left(\dfrac{1}{p} + \dfrac{1}{q}\right)$
• d$d(q - p)$