Answer:
p1s3: In my opinion, mobile devices are helpful for everyone because we can use them as a resource.
p2s1: First of all, people who are very anti-social in person tend to be more outgoing on screen.
p2s4: For example, when someone is shy, social media can help them feel more connected to others, because they feel more comfortable expressing themselves.
p3 last 2 sentences: For instance, there are times when someone wants the definition of a word they don't know, so they look online. In sum, mobile devices are not only used for entertainment, but as a resource for many kids around the world.
p4s1: Finally, mobile phones help people stay connected.
p4s3: In addition, social media can be used to keep relationships alive by staying connected through calls and texts.
p4s5: In a nutshell, social engagements are a very important part of relationships.
p5: In the end, many people...
I might add some later
Is it informal letter or formal letter
Serious and anxious would both work, but serious is more likely
I would say A but D could also be said softly
