The diagram indicates the direction of current through a metal block. Charge carriers enter the block via the face PQRS and exit from the face opposite it. The number density of charge carriers is $n$. Each charge carrier carries charge $e$. The mean drift speed of the charge carriers is $v$. Which expression gives the current in the block?
- A$envx^2$
- B$envxy$
- C$envx^2y^2$
- D$envx^4y$