A helium balloon is attached to a top-pan balance. A metal block with a mass of $100\,\text{g}$ is put onto the balance. The balance then shows a reading of $91\,\text{g}$. Which statement can be deduced from this experiment?
- AThe balloon exerts a downward force of $0.09\,\text{N}$ on the top-pan balance.
- BThe helium has a mass of $-9\,\text{g}$.
- CThe helium has a mass of $+9\,\text{g}$.
- DThe resultant downward force on the top-pan balance is $0.91\,\text{N}$.