Answer:
1. Testimonial evidence: The opinions of experts
2. This made the author's argument strong
3. The reason is that experts, more specifically, mental health experts are authorities in the field of mental/psychological stress. Therefore, their opinions on the effect of social media on teens can be regarded as accurate.
Step-by-step explanation:
In the article, "That's Not Progress", the author argued against the impact of social media on teens, describing it as negative. He pointed to the fact that social media made teens prone to depression when they are not acknowledged on those platforms.
He cited many mental health experts as evidence to support his argument. For example, he quoted one mental health health expert who said that 'a person's self-image can be damaged when unflattering images about them are posted.' This strengthens the reader's belief in the author's side of the argument.