C.
The introductory phrase, "Crowned with a wreath of olive leaves", is correctly separated by a comma.
The first sentence.
Ted and I cannot convince Steve to change, because he must first convince himself.
What is the prompt of the essay?
Essentially a thesis statement should state your opinion/the main idea of your essay. If a thesis is a question, it is no longer a statement.
Depending on what you will be writing about here are some alternatives that are close to your original thesis:
Social media has negative/positive effects on young adults. (discuss positive or negative effects)
Social media can affect young adults in a variety of ways. (discuss both positive and negative effects)
Young adults are affected by social media in many positive/negative ways. (discuss positive or negative effects)
