What are two common types of flower preservatives?

The correct answer highlights two common types of flower preservatives: sugar and citric acid.

Sugar acts as a vital food source for cut flowers, providing them with the necessary energy to maintain vitality and promote hydration. When flowers are cut, they lose their natural source of nutrients, so adding sugar to the water helps prolong their life by nourishing them and allowing for better uptake of water.

Citric acid is often included in flower preservatives to help lower the pH of the water, creating an optimal acidic environment that enhances the flower's ability to absorb the nutrients provided by the sugar. Additionally, the acidic conditions can also reduce the growth of bacteria in the solution, which is critical for preserving the freshness of the flowers.

Other choices presented do not effectively serve the dual purpose of providing nutrition and inhibiting bacterial growth. Water and salt, for example, can create a very different environment that isn't ideal for flower preservation, while vinegar and baking soda produce a reaction that doesn't support flower longevity. Alcohol can be harmful to flowers, as it can interfere with their ability to take up water. Hence, sugar and citric acid are recognized as effective components of flower preservatives, making them a standard choice in floral care.