A wooden block with density $\rho_w$ has side lengths of $a$. It is immersed in a liquid whose density is $\rho_L$. The upper face of the block lies at a depth $h$ beneath the liquid surface. The acceleration of free fall is $g$. What upthrust does the liquid exert on the block?
- A$\rho_L a^3 g$
- B$\rho_w a^3 g$
- C$\rho_L h g$
- D$\rho_L a g$