The central idea is the same as the main idea. Most of the time, the main idea is mentioned in the Title. Without reading the essay, I do not know what the central/main idea is.
Answer:
Plants
Explanation:
They make food from sunlight, CO2 and H2O. This process known as photosynthesis
I think it would be either C or A, but I think C is more right than A
Spotless
An adjective describes something, so the kitchen is being described as spotless
