Explanation:

- Option 1: A negative slope:

- Correct Answer: In the case of normal goods, the demand curve typically has a negative slope. This means that as the price of the good decreases, the quantity demanded increases, and vice versa, illustrating the law of demand.

- Option 2: A positive slope:

- A positive slope in a demand curve would suggest that as the price increases, the quantity demanded also increases, which is contrary to the typical behavior of normal goods.

- Option 3: Zero slope:

- A zero slope would imply that changes in price do not affect the quantity demanded, which is not common for normal goods.

- Option 4: None of these:

- This option would apply if none of the provided options were correct.