Answer: symbiosis is not always mutually
Explanation:
Introductory blurbs often contain valuable information. They'll always provide basic information about the passage, like title and author name, but they can also contain important definitions or pieces of useful background knowledge.
Answer:
The photosphere is the visible surface of the Sun that we are most familiar with. Since the Sun is a ball of gas, this is not a solid surface but is actually a layer about 100 km thick (very, very, thin compared to the 700,000 km radius of the Sun).