Sarah has just come to understand that seeing a dog will make her best friend thrilled (she loves dogs) but her other friend afraid. given that sarah has just developed the ability to understand that the same thing will make different people experience different emotions, how old would you hypothesize sarah is?

She is about 7 to 11 years old. This is the concrete operational stage. During this stage they begin to become less egocentric and begin to realize everyone is unique and may not sure the same thoughts or opinions. This is listed in Piaget's
Stages of Development.

filamentous algae

According to 2 sources

Spirogyra is a filamentous algae, commonly found in freshwater ditches and ponds. Go through this article for a brief overview about these algae. Spirogyra is also known as pond silk, as its filaments shine like silk due to the presence of mucilage. The outer cell wall has pectin which dissolves continuously, thereby producing the mucilage